Exactly my thought. Why I host one for pop music. Real quiet now, but provides an easy gateway of members who only live in those few subs (and mainsubs) to join, and it's one I'm happy to host. There are dozens, probably hundreds of subs on Reddit under that umbrella, I think that warrants an instance.
Same with other general topics. One specific to gaming, one to sports, one to types of beer, idk any general subject I think can be an instance