It was invite only, not open registration, so not surprising they didn't have many users. Although Bluesky is the same and that seems to have loads. Hmm.
I had an account but literally used it for five seconds and then largely forgot about it.
I think it should take for someone to make a mastodon instance that just doesn't boast about federation yet is federated for this to take off more. People say "join mastodon" or "join lemmy" but then you're hit with a list of servers and you just give up. Contrary to something like "join talkfunhouse.com" which is actually a federated instance