You are asking the wrong question. They do it because they get views and make money with it. The better question is: Why do people watch this stuff?
Have you looked at politics or social media in the last decade? It just works! Because most humans are morons in search of convenient answers. They want simple stories that divide the world into good and bad, light and dark. They might have a hunch or a pre-existing belief or one side of the coin is particularly advantageious to them and they want that belief affirmed and never questioned. They want to feel smart, like they've known it all along. The world sucks and is super complicated - most people don't want to bother with it. Ah, must be evil [insert random out-group here] that destroy it for us righteous [insert random in-group here] instead, clearly that's the answer to it all.
People love a good boogeyman. It was jews, alt-right neo-nazis, SJWs, white nationalists, commie trannies, racists, women, men, etc, etc. Yes, Reddit is evil, so is 4chan - just depends on who you ask. There are people who think these are actual problems instead of made-up tribalism to manipulate them. I think it boils down to lazyness and lack of education in critical thinking.
