Huh, wonder how they went from communism to authoritarianism. Well, surely that was a one time coincidence and not indicative of a systemic failure of communism as an ideology.
No one does, because stupid ideas, in order to keep adherents, have to become protean. Every time someone points out an obvious flaw in your ideology, you'll say "that's not what it is" and shift it to something else.
I can tell you what it really is. You won't like me telling you. It's angst. It's rebellion. That's all. You'll probably grow out of it.