I think the profit motive is literally destroying the world given the climate crisis, as well as destroying everything good or useful about the Internet. So I think figuring out how to do things without the profit motive is the only way forward, as impossible as that might seem. Surviving capitalism with that attitude may be challenging, but we don't have a future under capitalism anyway.
I think that if the value of social media comes from the network effects, then it's not a question of whether you can find some core of users who consider it more than a hobby. (Ugh, you want a network for professionals for whom it's their job?!) For social media to reach its maximum value, it has to reach literally everyone, and at that point you're talking about something that ought to be a government service, like the postal service. For smaller networks that are less focused on reach, maybe hobbyists are the ideal providers.