I’d doubt this is a thing that’s unique to Lemmy, but A) moderatorship in general attracts a certain kind of individual and B) Lemmy as a whole seems to attract a user base with a fairly consistent mindset which tends to be overall left leaning and a little bit radical. A lot of the normies are probably still on reddit, or wherever the fuck.
…Says the chump who moderates three communities (one of which is dead), so everything I say on the matter may be bullshit.
There are exceptions, like the various infamous tankie instances. The thing about Lemmy instances is anyone with thumbs and a credit card to pay for hosting can create one and then make it their own ideological hobby-horse.