That's an issue, but I don't think that's the main issue. There's plenty of ways around that if the will is there. Worst case scenario you could just create an old-school mailing list. Everyone has the infrastructure for that already in place, and plenty of close communities were built around them ~30 years ago.

However, there's two big things standing in the way:

1. The vast majority of the population - I'd say at least 99.99%, probably more - is only interested in jumping on the next big thing. People who liked and enjoyed being part of mailing list communities, handcraft html webrings, AIM, self-hosted forums, MUDs, etc. would probably be happy to go back to those if they were suddenly popular again. But when they went out of popularity in favor of current social media trends, everyone jumped ship. Everyone's following the crowd.

2. Online communities tend to not place any limits on output, so a few hyperonline individuals dominate the conversation (and in cases where moderation occurs, have methods to control the community). Hyperonline individuals don't tend to be the best socialized ones (people with healthy lives aren't spending all day on the internet).