While I agree with your vision, I wouldn't be so quick to dismiss this. I've tried for decades to get people onto open platforms with me. Tooling pain doesn't help, but by and large, the issue is critical mass. If I were to drop out of <major communications platform here (currently Discord)>, no one would follow me except for my wife. I'm not really speculating, I know this to be true because I have tried it. Several times.
You can see it outside of close social circles as well. At one point my condo association leadership decided they wanted to shut down (well, at least abandon moderation of and cut all ties with) the community Facebook group, and bring our web presence up to modern standards. We built out a website, with many features we felt would be useful --- membership directory, community knowledgebase (some questions just repeatedly come up over and over again), a forum for community discussion... and nobody used it.
The reason? Turns out it was nothing to do with our implementation. It just came down to the fact that Facebook was already installed on people's phones, and they already spent their time there. That's it. Inertia and critical mass.