A large enough userbase to support more niche topics. On Lemmy, like a lot of small communities, people tend to put the cart before the horse. They make places to share content for very niche topics but there aren’t enough to warrant it. Plus sometimes you have mods in certain relatively niche groups that will remove content from their community because it is off topic, but their volume of posts is nowhere near enough for the occasional, technically off topic post to really matter. I see it in Discord servers too. Some places have more channels than users on the server. People get obsessed with categorization.