The reasons are explicable but they are very difficult to understand without a thorough knowledge of how economies work.
GLORIA ALVAREZ ON REASON TV: Socialism Fails Every Time (Video):
It certainly has a lot of bad luck associated with it, for some inexplicable reason.
For an explanation, you need to go to what is known as the Socialist Calculation Debate, and then be prepared to spend a long time thinking it through. You can easily see that all such experiments have failed in the past, but that is empirical, and never convinces since it is always different next time, at least when it all begins. The end point is always The Soviet Union, Cuba, North Korea and Venezuela, and never Denmark or Sweden, but why?