This article attempts to bite off a lot! I'm going to condense it down to one small part.

The Dark Forest experience that's causing "mass migrations" on the Internet is that, if you venture out into social media carelessly, you're entering an aggressive and frequently unpleasant space which is close to the opposite of "fun" for the average person. Here follows a laundry list here of things which you might expect to encounter in an unpleasant online space, most of which have a kind of tabloid quality: scams, nonstop sales pitches, porn, extreme violence, celebrity worship, ideological extremism, racism, sexism, etc. And more (that list is not exhaustive).

So people find that signing up for the average generic platform that welcomes everybody is a bad experience, and migrate to more niche ones. That's been the path I've followed too, all the way here.