That’s a good question. From what I gather, Lemmy (and most of the Fediverse) is an alternative to something, with less focus on the money/advertising. So I would guess most people are looking for an alternative way to connect about common interests. And because it’s not the easiest path for social media, I would guess most people have a desire for agency/self-reliance.
And because the whole Fediverse seems to be a different way of approaching social connecting, it takes a little more understanding of computer technology, so I would also guess most people have a least a higher than average affinity for computer technology. Linux and Programming Humor are larger communities.
That said, I have enjoyed a somewhat active participation about woodworking, gardening, jokes, news, medical updates, etc. Like mentioned in another comment, the different instances will have somewhat different norms and practices.