Political Theory: What caused communism or socialism to fail?

I see three main factors; inability to plan the economy, lack of motivation and dictatorship.Inability to plan the economyThe command economy works with an idea that you can predict what and how much the people will buy. Therefore you produce only what you need and no surplus of useless goods.But it wasn't working. People buy some stuff because they do it every day (e.g. bread for breakfast) or because they have to (gas for cars). You can perhaps predict that. But other things are bought completely randomly. And you can't predict that. Therefore what follows are periodic random shortages of various goods which is something that everyone who lived in a socialist/communist state is familiar with.Lack of motivationWhen you invent something in capitalism you have it patented, you can find your own company and get super rich. In socialism/communism when you invent something you get a medal and that's it. If Mikhail Kalashnikov lived in a capitalist country he would've become a multi billionaire and CEO of his own giant weapons company. But he lived in a socialist/communist state and received almost nothing.Basically the people weren't properly rewarded for their additional activities and ideas. They got only medal. That worked when the people believed in the goals of the regime. When they stopped believing the stopped striving. And the economy and worker's productivity suffered because of it.In capitalist countries when you strive you get more money. So the people strive hard.DictatorshipPeople like freedoms of expression, travel etc. And democracy gives that. But socialist/communist state doesn't since it's a dictatorship.People can be happy in a dictatorship but as a compensation for the limited freedoms the dictatorship had to offer something; a nationalist feelings of pride, better economy etc.Socialist/communist states never managed to offer an alternative. Better economy? No way. Pride on the regime or country? That was limited and would work even in capitalism.And once the people visited Western countries they found out how miserable their own lives are. They stopped trying to help the regime and only tolerated it. And once the regimes weakened and/or people got bolder the regimes have fallen. 

The problem with communism and socialism is that the real power is consentrated in hands of burocracy. They decide what  and where to grow, plant, produce and how to distribute. This system will never be stable in terms of math if the outside restrictions would not be put on the type and quantity of consumption. It is awful. At the end of 80th in Moscow there were only three ultrasound diagnostic systems (for more than 6 million people).