"Why do anarchists live under capitalism if they hate it so much?"
Bro, sometimes you don't have a choice. They might not know about Lemmy or other Reddit alternatives that aren't corporate owned piles of dogshit. For a while, there weren't any; that's why I was there for so long.
It's also hard to just up and leave a community. Even if it's in a bad neighborhood. Your friends are there. Unless they come with you, you're much more inclined to stay.