You act as if it's been tried any amount of time that would be statistically significant. Sometimes it's not even communism other than in name and folks still count it.
And it doesn't devolve into it. It's simply always been done at the same time. When you have essentially a dictatorship, absolute power will corrupt absolutely.
A practical distinction historically speaking, but not philosophically speaking. If you're unable to differentiate between concepts in history, I don't know how you can ever effectively discuss them objectively. Though, this should have been evident with your comment initially. Communism doesn't devolve into authoritarianism. They're not even the same types of philosophies. One is about governing and one is about commerce. It's like claiming capitalism devolves into a plutocracy. It does help to produce a plutocracy, but it didn't devolve into one. They're not the same thing.