I have a feeling some of those people are the "Fediverse is too confusing!" People, yet they don't even try.🤦♂️
It can be that way, but welcoming people could also be scaring them away.
On FB I've joined groups to see that once a month the admin posts a "this month we welcome"-post, which lists and tags every new member. Every single time I've seen that I've noped out and left. Just let me creep in peace and quiet, and maybe I'll join in ... eventually.