The default view for communities is Local, which will only show communities on your instance. Given you’re on lemmy.world, that’s a considerable number, but if you click ‘All’ at the top of the communities page, you’ll also see communities outside of your instance (but again only ones that your instance knows about, which amounts to any that someone from your instance has subscribed to). Again, you’re on LW, so this is a significant percentage.

If this is a niche that doesn’t exist currently (or you can’t find a place for it), you could create such a community.