Why are train stations nicer than bus stations?

Train stations all over the world were built at public expense during periods of economic expansion. When they were built they were symbols of the city's prosperity. The train stations of Paris are as elegant as the rest of the city and still in daily mainstream use. The train station in Zurich used to have 3 good restaurants and a movie theater. It still has trains departing for exotic locations, exactly on time. Trains in Chile were the main way of transporting both people and freight. They were built in the mid 1800's when this was true of most countries. Bus stations in Brazil are dirty crime-ridden places.They always were. The same is the case in the US. Trains were replaced by planes in the US long ago.The difference between train stations and bus stations in the US is not as obvious  as in Europe because train stations have fallen into disuse. Train travel used to be an elegant way to travel. It still is in Japan and Europe. Buses always were in private hands and they never spent any money on the terminals.

To add to other answers. Train stations are generally built at the same time as railways and are thus and integral part of a HUGE capital expense and often by governments. To spend £150m on a station as part of a £10bn railway project wouldn't seem crazy. Bus stations are not attached to any particular company or scheme and the investment levels are in comparison tiny. To start a couple of new bus routes and a mini network may cost £10m so to contribute even £1m to a bus station is crazy-  It's not like roads were also built at the same time. Therefore rail stations are often civic cathedrals acting both a temple to the triumph of the railway construction and also as a impressive first impressions to the city and with relative large investment levels possible.

Platforms are longer, and the vanishing point of the tracks add to visual appeal Trains have multiple boarding points and hence the crowd is more evenly distributed The turnstiles and escalators give off a feeling of order Boards indicating where a particular coach would stop and punctuality add more charm to train stations This perception of course depends a lot on what region and station you use.

I am not sure whether "airport terminal" and "cozy" fit in the same sentence without a negation, but so be it. As it has been said, train stations are build in conjunction with building or upgrading lines, and therefore part of bigger projects. Maybe not the biggest stations, but mid-size stations were also the home of the station master, someone rather high up in the rank of the railroad, and therefore the whole thing was made to the according status. On the other hand, bus stations were and are rarely owned by the operator, and there is not really an incentive to "represent". The overall cost of a bus station is lower because it needs less space. A bus station can be moved easier, which also means that the incentive to build something representative is much smaller.

In St. Paul, the historic Union Depot has opened after a huge renovation, but only buses use it.  The same thing with Denver Union Station.

Actually,  I would argue that many train stations, at least in the US, really are nicer than bus stations. This is since many train stations in the US were built in the days when railroads took pride in their appearance, and passenger service was the railroad's public face.  Furthermore, many railroads were highly competitive with their neighbors, and would try to out-do each other with nicer stations and better trains. though many stations have been replaced with "minimal" platforms and such, quite a few of the old stations and terminals are still operating since the days of the steam locomotive.  Bus companies on the other hand built their industry on economy and flexibility.  a spartan bus station was cheaper to operate and maintain, and kept ticket prices low.  Its like the difference between a nice restaurant and a fast-food place.   They could make a Burger King look "royal",  but that would run counter to the purpose of the establishment.

In those parts of the United States where train travel still accounts for a significant share of intercity traffic, the surviving grand railroad stations - all built by the private railroads that served them, or in the case of "union stations" as in Washington, Boston and Chicago, by consortiums of railroads or companies formed for the purpose - have been either maintained or restored to their original grandeur. (New Yorkers have one such station, but the other was obliterated in 1963 and a sports arena built atop it.) All of these are now publicly owned and the restorations financed by public funds. Bus terminals in this country, like in most others, are built and maintained by the bus lines that use them. As the passengers tend to come from lower rungs on the socioeconomic ladder than train passengers do, they also tend to be less grand. However: in Boston and Washington, the main intercity rail station is also the main intercity bus terminal, so bus riders there enjoy more attractive facilities.