Because communism is a populist concept a fascist sells to poor people who don't own anything, like nazism and anarco capitalism is a populist concept sold to middle class who own things.

Alright, it's inevitable so I might do it first and especially before Immortal Scientist ☭:

He sure didn't help, but there is a lot more behind it. Communism is fundamentally flawed because humans aren't ants, which makes communism only possible through violent repression and a revolution that implies that those on top of the pyramid step down afterward. And of course, they never do.

A communist revolution grants absolute power over the economy and the minds of its citizens, and absolute power corrupts absolutely