This is a concern, but luckily this isn't required. I set up hobbit.world to host my Tolkien related communities. It only costs $6 a month plus the $35/yr for the domain name to host a tiny instance like this. I don't need to depend on anyone but my hosting provider.

To be safe I should download backups once a month or so.

But the point is that for big communities that people put a lot of time into, there should be an instance for each one owned by one of the mods.

Edit: Meant to reply to the person concerned about the centralization of communities.

The community here is already 100x better then anyone I've communicated with on Reddit

c/showerthoughts

…the other 50 who showed up had to stand in the hall or not get in at all. They said the venue sucks and left.