The communities I browse are either small (behavioral science/school) or full of elders who aren’t interested with switching platforms. So that’s a pretty big reason. Some of them have organizations that still have large presences on things like fb. Not having an account hamstrings a persons ability to stay current with professional topics…not great for a lot of fields. Now, this is just my particular instance. But I’ve heard a lot of the same from colleagues and adjacent professions. As for me, my account is deleted and I don’t contribute content meaningfully anymore. Which I suspect is another major downside to all of this, brain drain.