Why has German culture failed to preserve itself in American society?

No culture has "preserved" itself in American society.  None.  The nature of the melting pot is that the contributing essence melts into the larger entity while altering the whole simultaneously.  Mexicans, Jews (Sephardi and Askenazi), French, Irish, Indian, Chinese, African, German/Amish, Italian, Arab . . . whomever.  None come here and remain true to their roots.  None.  Zero.  Zip. Within a few generations, they melt away into the whole of America, shifting the whole slightly at the same time.  But rest assured, in the case of Germans, the "whole" changed more dramatically than any other immigrant group save the British and the Irish.  They may be surpassed by Mexicans and Indians before long, but at present, they are one of the "big three" immigrant groups that completely altered the nature of who the USA is. So, I'm a bit confused as to the nature of the question?  Is it about "communities" or "islands" of Germans like those in Russia and Romania that never assymilated and instead formed pockets of those holding on to their identity?  If so, that's because neither host society was amenable to the German people, their culture and/or their names.  The USA, being an immigrant society, was unbelievably welcome to Germans who--by the third generation--typically considered themselves wholly American "of German ancestry" and nominally that to boot.  World War One and World War Two only hastened the already inexorable muting of the large German identity in the US.  It was happening long before that.  By 1910 the massive German influx to the USA had all but tapered off.  It was only a matter of 30 years anyway before the German identity in the US began to fade into the background.  The two successive World Wars just sped up the process a bit.  Any shame felt from those wars quickly wore off thereafter.  The USA, with a bit of noted prejudice, openly celebrates and epitomizes the German immigrants to the point where by 1950 nobody much questioned their German ancestry. I grew up in the heart of "German America".  My neighbors went by names like Sprauls, Sheimann, Neiger, Christianson, Kaiser, Volk, Keller, Klein, Junker (pronounced with the Anglo "J" not "Y" sound) and Hamburg.  My street was peppered with those names.  We celebrated Oktoberfest (in October, though).  We went to our Lutheran Churches (one of the biggest churches in Northern Ohio).  The smoldering embers of German heritage will remain smoldering within the American furnace for as long as there's a USA.  The reason why it may seem like you see a lot of Indian, Chinese, Mexican, Hispanic and African influence in the USA is a combination of recent massive influx thereof and (in the case of Blacks) a recent revival of a long suppressed cultural heritage that many are now trying to assert in the tapestry of who the USA is.  Two massive immigrant groups:  Hispanic and Sub-Continentals (India, Pakistan, Bangladesh and Sri Lanka) are the "big ones" recently.  Asians -- on the whole -- for the first time in history were the largest regional immigrants, passing Hispanics in 2012.  Asians aren't a monolithic group, but it's still a notable shift.  Dropping birth rates in Latin America, growing economies, stable governments and reasonably free nations ensure that the driving force of immigration to the USA will wane over the next decade, to be replaced with Asian and likely West African (Nigerian, esp.) immigrants to the US. It's always "the recent ones" that seem to be heavily noted.  They are "new" and new looks obvious and odd (to chose a un-delicate term).  Germans have ceased their massive influx for a bit over a century now, so they are no longer any different than the Irish or British immigrants before them.  They just are a footnote in history, lots of last names and some cultural nuances that we now assume are "normal".  The Indians and Hispanics are the new guys, so it's easier to take note of them and their changes to the American landscape. But rest assured, back when the Germans were "the new guys", people hated them.  There were comics that depicted them as disease ridden, anarchists, Huns and criminals.  Invading hordes and pointy-helmeted anti-Americans.  The German immigrants in their day were treated, frankly, FAR WORSE than their descendants now currently treat the Mexican immigrants.  Back then open prejudice was very much in vogue and people openly considered Germans (and Irish) to be pests.  Look how that turned out!

While not as detailed as some of the answers here, it seems German culture hasn't been preserved separately in the US because it is so mainstream as to be invisible. Go to a baseball game and you'll have a Frankfurter and a Coors beer. These are obvious examples since the names are preserved, but in many ways, small and large, American culture is steeped in German culture. If you took everything German out of mainstream American culture I doubt you could still recognize us.

German culture has experienced periods when it seen as being "Un-American" by some. But it has never faded from the American mindset. The Amish, Mennonites and Anabaptist communities in the US all speak a form of German among themselves. Their surnames are German,as are many of their written and oral traditions. Many Jews in the Northeastern parts of the US still speak Yiddish, which is a German language developed from Ashkenazi Jews from Germany and Central Europe. Every major city has at least one restaurant which serves German food. Many cities celebrate Oktoberfest, a celebration with origins in Germany. The largest portion of US immigrants to the US were from German and Germanic origin in Central Europe. While German culture may not have infused the American culture in the way that Spanish or Mexican cultures have, that may be because of lingering antipathy due to the two World Wars and to the proximity of Latin cultures to the US. This basic premise of this question seems to be flawed.

There are many German-American groups in the US fighting the trend.  Unfortunately teaching German in the US is a losing battle with the domination of English on the internet and the willingness of Germans in Europe to expand their knowledge of other languages including English, French, and Chinese. Some groups preserving German culture are: German-American Committee of Greater NY, organizers of the 50+ Steuben Parades, the Goethe Institute (promoter of German Language), the Heritage Museum in Washington DC, and other groups. http://GACgny.org http://SteubenParade.com http://www.goethe.de/ <a http://goethe.de> link</a>

I regard assimilation as neither good nor bad. I think there is a linguistic aspect to it. German is reasonably close to English, and English grammar is more straightforward, even to us. Germans who speak English to other people all day get worse at speaking German over time, they simply lose the feel for the other language. A friend who emigrated to Australia in the 50s told us that the first generation still spoke German at church, the second generation only did so occasionally, and the third did not speak German at all. Germans and other Americans of European origin are not so different, culturally, that there are significant barriers to intermarrying and socialising with the other groups. My own family, who emigrated to Poland in the 1700s, stayed a visible minority and spoke only German among themselves up until the late 1940s, when they, uhm, emigrated back. This was partially because they were Protestants, which set them apart from the Polish population, and was a far bigger dividing factor then. German emigrants who came from catholic parts of Germany were far more likely to intermarry with the Polish population and get assimilated.  In Europe at least, the idea of a nation state with a largely homogenous monolingual population only became popular after Napoleon.  Up until then, I don't think there was as much of an expectation that minorities should assimilate, since the different European countries were not necessarily even governed by nobles of the same nationality.  Even after the emergence of nation states, the pressure to assimilate was stronger in smaller countries, such as Poland, than in the larger ones, such as Russia, which was home to many different minorities that spoke languages other than Russian. About the second part of your question, I think all western societies are trying to navigate the narrow path between nation states and multicultural societies - maybe even post-multicultural societies. Germany was naturally more reluctant to foist a German cultural identity on their immigrants than the US, which has a more positive self image and has traditionally been a nation of immigrants. This may have been either carelessness ("they won't stay forever anyway") or well-intended - "we have no right to impose our language and culture on immigrants" - but it turned out to have negative consequences. A good portion of our third-generation Turkish immigrants neither feel completely at home in Germany nor in Turkey, and some of them have difficulties speaking either language correctly. The way the US has traditionally promoted at least a basic level of cultural assimilation of their immigrants seems like a better deal for both the immigrants and the existing citizens to me. (I assume this is only even questioned now because Spanish-speaking immigrants have hit a critical mass where the English speaking former majority feels threatened by them). Our government is looking to course-correct on this issue, but I'm afraid we won't be able to replicate the success of the American model.

During WWl and WWll Germany was the enemy. H.L. Mencken, in diaries left to the New York Public Library, stated he wished his family had remained in Germany given the amount on anti-German feeling in the US. It was easier for German immigrants than say Asian or African immigrants to assimilate and they had every motivation to do so. My grandfather had a factory making parts for the Air Force during WWll. To the extent he could get away with it he only hired workers with German or Swiss backgrounds. This was in Lancaster, PA. He was Swiss and spoke German at home. His grandchildren run factories in China and Brazil and do not speak German. German culture runs toward conformity and rigidity, Brazil toward adaptability and informality, American mainstream culture is somewhere between these extremes.

Yes, it's the natural course, and past assimilation looks quick only in retrospect. WWI hysteria hastened the death of German education preserving literacy in American-born generations, but Latinos have never made such an effort in the first place and US-born Latinos rarely maintain Spanish reading and writing skills. English-dominant speech skills are universal for the American-born and educated of all eras and ethnicities.

I think that it started with the world wars, at least in Davenport, IA, many immigrants who still spoke German in their homes stopped after the United States entered the war in 1941.  Presumably because they were either afraid or ashamed of their homeland.

During WW1, many German-language newspapers (and there were tons) were forced to shut down.  WW2 saw even more pressure to remove German as a viable language in US (surprisingly, there was similar pressure on French in Maine).  Many Philadelphia public schools used German-English textbooks (German on one side, English on the other) till the outbreak of WW2. After WW2, knowing German was considered taboo.  And that is how German culture in US was reduced to drinking some pathetic beer and eating horrible hot dogs.