Maybe we could say that advertising revenue is toxic to community spaces? If they really want to be the town square, well nobody wants a town square that’s primarily billboards and advertising. People who actually live in New York don’t go to Times Square, and there is functionally no actual community there.

As an counterexample, Discord specifically is trying a subscription “free-to-play” model. I think this could work pretty well for future sites - a little more expression or some cosmetics to make you stand out, but still a very usable and unobtrusive service.