If I had to guess, at least a good fraction of them are communities people duplicated after the initial Reddit exodus. At that point there was a lot of people trying to establish communities directly carried over, but if they failed to launch then they've probably been left to rot.

Maybe community name scalpers.

When a service goes from "nobody will probably use this" to "this might get big" and it has unique naming capabilities, some people register a lot of them to eventually sell them off.

I made one for my hobby just so anyone coming from Reddit would already have a place to land. If anyone asked for the keys I’d probably give it for the fun of it. I posted a half dozen times and got one or two responses.

The reddit migration. A lot tried to remake communities here and they just never got traction. I have one like that.

If you build it, they will come.

Look at the name of this mod for one a Community called bandaid

ADHD