Which is just absolutely full of spam now, plus you need to pay for access (largely).

Usenet has/had hundreds of millions of active users?!?

That's certainly news to me.

I can’t find anyone who says how many users, but 110-120 thousand newsgroups.

With a tenth active users and ten times the spammers!

How about "email"?

Do people forget it's a common protocol that isn't monopolized by anyone and is the widest prevalent even today, perhaps because of it?

I don't think many people consider "email" to be a community in any meaningful way. The same way people don't consider physical mail, the telephone network or the internet as a whole a community.