Chances are that Lemmy has about the same makeup of people as Reddit, mostly. I’d say that where the difference lies is in the amount of tolerance they have for Reddit shenanigans.
Stupidity on the internet is amplified with resonance. One says something stupid, trolls or being rude, the other responds and the intelectual level of the discussion is plummeting. So my theory at least is that there’s about the same percentage of “stupid”. We just haven’t yet reached critical mass.
Facebook kind of died and used the momentum it had to reinvent itself. Back in the day I used to see updates from my friends, and I used to interact with them. I stopped using Facebook at some point a few years ago and recently got back to it. I use Marketplace, and in my country people with the same hobby as me seem to interact over Facebook more than anything else. Younger people rarely upload except for a few very active outliers. Most of the content is these clickbaity short videos of 5-minute crafts or live-feeding frogs to slightly larger frogs because Facebook thinks I'm into it for some reason. They just made an addictive never-ending stream of content.