Something I realized: If you visit a community on a different server, it doesn't show all subscribers. Like on Feddit.de, it tells me that there are 993 subscribers for this very community. But if I visit lemmy.ml/c/memes it shows that the community has over 18k+ subscribers. Maybe it only shows the subscribers from your own instance? Like 993 People from Feddit.de are subscribed to this community? No idea.
Since you're registered on lemmy.ml, and thus probably viewing everything through that, I think you only see the subscribers on lemmy.ml. Most people and comms are now at lemmy.world.