I joined Lemmy a few days ago and have been reading around. 90%+ of the content I see, even on non-politics related communities, is political in some way. I have no interest in that, so it’s tiring, especially when it’s inserted in the comments of completely unrelated posts.
Lemmy was originally founded by political extremists who wantted a space for their politics (tankies.) Its since grown past that, but that inflence is still present in many ways, most prominently in the influences of .ml. On top of this, politics is something inflammatory (and thus engaging) that affects everyone. Because its both engaging and broad-appeal, its going to be something everyone talks about. On the other hand, many niches, aside from being niche are often less inherently engaging (IE talking about a finished TV show). This makes it very hard to get the critical mass needed for a community to snowball into relevance. This means that (effectively) all you’re left with is the political communities and a couple niches that are broad appeal enough and have active enough users to be stable.