The trolls and fascists do not exist on Twitter to hang out with other trolls and fascists. They're there hunting for liberal tears. When their prey leaves, they follow.
Bluekky has been open about not moderating their platform. They've provided users tools to not see the shit they're letting through the door -- which, yes, is currently better than Twitter, where the current ownership believes that 'free speech' is deserving of a captive audience -- but if the bsky algorithm thinks you have something -- anything, really -- in common with the Nazis, they'll get shunted into your timeline, leaving you to play wack-a-mole.
It's really showing the huge issues with fediverse monoculture, too, that is driven in no small part by Mastodon. Mastodon is designed with very limited theming, very limited ability to self-brand, etc. It's designed so that every Mastodon website looks just like every other. This gives most people the impression that Mastodon is a place on the Internet, in the same way that, say, Facebook is, rather than a website platform like WordPress.
The magic of being able to see what people post on other websites from the one you're using gets totally overwritten by the expectation that everything is actually the same place. And once you have that expectation, Mastodon kind of feels broken. "What do you mean I can't see all of the comments? Why not?", "What do you mean you're denying me access to those people over there?", etc.
And don't even get me started on the people lobbying for limited functionality because they want to own the commons and dictate how people use the public and open communication protocol.
It's all so frustrating, and sad.