I think the biggest reason coming off mainstream social media is so good for mental health is they're built mostly on negativity, especially in the last few years. Think about it, you're scrolling your timeline, you like something you hit like, thumbs up, upvote or whatever but most sites have removed the ability to downvote, dislike, thumbs down so the only way you can say you dislike a thing is to comment on the thing, by commenting your dislike you're putting yourself in the middle of people who mostly like the thing and who feel like they must defend the thing they like.. and BAM, bullshit central. This is something I think about whenever I get the urge to get myself unbanned on Twitter, so many came here, said they loved it then a week later went back to pissing into the ocean of piss that is Twitter, it's really not worth it.