Federated sites overlap with leftist-adjacent interests. Software freedom, opposition to Facebook, weird illustrated porn, that sort of thing. Even if we're not leftists - we're the people who heard about Lemmy and went "oh, like Mastodon."
Many leftists were also familiar with Mastodon, because they saw Twitter as a harassment engine. Every system is perfectly designed to produce its observed results. Even before Elmo took over, Twitter was a continuous source of misery by design, if not on purpose. Now it's definitely on purpose. And it's been tilted against leftists, specifically, for a long damn while.
Some people are here because the mainstream options were a threat to their physical safety.
Meanwhile, right-wing assholes aren't leaving Twitter until they run out of victims. They just want an outgroup to yell at. They don't even like alternatives made for them specifically, because they can't stand each other, either. When they get tired of suffering their own company they'll migrate over to Threads. And then endlessly whine that Threads is "bias" against them, no matter how blatantly Zuck ignores their abuse and silences their victims.
Reddit was in a damningly similar situation, long before Spez decided to burn down every scrap of trust and goodwill. Some of us have been waiting on a better alternative for ten fucking years. There wasn't one. There still isn't. The bastards in control just made reddit itself worse, in ways that make even passive use feel like a failure and a betrayal. Spez could personally hunt me down and kick me in the groin, and it wouldn't leave me any less likely to waltz back in with a smile on my face. Dumb bastard made insane demands, killed the best interfaces, told us stupid lies, threw away our money, declared protest powerless, and threatened the people who do all of the fucking work on his empty box of a website... then says 'they'll come crawling back.' Nooo shit the first people out were principled self-organizing curmudgeons.
That aside:
People here reasoning from what they pretend "conservative" must mean are actively doing harm. Political conservatism obeys none of the other dictionary definitions. It's just a label. It's the label chosen by generations of influential public figures whose general philosophy is "Well someone has to be the king." That is their only constant, and it is a thought process baked into the human brain. It is our default. That's why dealing with it is such frustrating bullshit.