Greed is a big factor. Communism will be possible one day in the future through technology, but we're not there still IMHO. The "fully automated luxury space communism" meme might not be such a meme a thousand years from now.
That said, communism in small scale societies and communities works. In large scale, money and trading works better.
There's a lot of reading I'm doing on this topic, so don't take my word for gospel 😄 it's been fun chatting with you about this stuff