You know, if I've noticed anything in the past couple years, it's that even if you self-host your own site, it's still going to get hoovered up and used/exploited by things like AI training bots. I think between everyone's code getting trained on, even if it's AGPLv3 or something similarly restrictive, and generally everything public on the internet getting "trained" and "transformed" to basically launder it via "AI", I can absolutely see why someone rational would want to share a whole lot less, anywhere, in an open fashion, regardless of where it's hosted.
I'd honestly rather see and think more about how to segment communities locally, and go back to the "fragmented" way things once were. It's easier to want to share with other real people than inadvertently working for free to enrich companies.
Another part of me though thinks differently. We are a species that builds knowledge from generation to generation. From one person to another. Over years, over centuries.
Philosophically this part tends to think that your thoughts and ideas belong to humanity and thus need to be shared with all of us.