I think because people are the same no matter what platform they're using and you'll end up with the same kinds of arguments, trolling, or derailing everywhere. But they already have platforms they're on for those, so why switch?

Lemmy would have to be pretty different and because humans are the same everywhere, I'm not really seeing that difference.

I see it somewhat when browsing contents in other languages because the culture is different enough to lend itself to different contents, or at least different arguments that are less tiresome than what I see on English platforms...