Differences in policy. There are wildly different ideas about what is and isn't acceptable.

> Sure, you can pick a random one like fediverser.network apparently does. Looking at one line from the list, I see that r/manga points to ani.social/c/manga which has 561 subscribers, when lemmy.ml/c/manga has 3,480. What?

That's not random. There was drama. The lemmy.ml admins are hostile to a lot of anime-related content and drove off most of the community that was accumulating there last year. ani.social is where the active, non-tankie communities are now. It's run with what seem like fairly reasonable policies and actually welcomes the subject matter. If you were relatively happy with the handling of anime-related content on reddit a few years ago then the communities on ani.social are probably what you're looking for; it's a good recommendation.

Lemmy.ml was the first instance, so naturally many people created communities there before. This does not mean that it's still where the anime fans want to congregate. The admins of lemmy.ml also said that they want to promote decentralization so they want as few communities there as possible.