Yep, places with more people will have a wider range of communities in their "all" feed.
That said, the barrier to making an account isn't too high. My first account was on Lemmy.ml back in 2020, shortly after Lemmy was created (I never stuck around and left pretty quickly).
Last month I realized I don't trust Lemmy.ml, so I joined Beehaw.org.
Then I thought Beehaw.org was a little overzealous at times, so I came here to Kbin.social.
I've largely stuck to Kbin because I really like how it looks and feels, but I did make accounts on Lemmy.world, fedia.io, and sh.itjust.works as backups in case Kbin goes down.