Very, very few people care about privacy to a meaningful degree, even if they (loudly) profess that they do. For communication apps specifically, there's also the network effect problem and having to deal with the increasing proliferation of government speech laws (Online Safety Act and what have you).

If you just want to make a buck, build a ChatGPT wrapper where people will pay you for the privilege of uploading their deepest secrets and intellectual property to your servers.

If you're ideologically motivated, forget about the profit motive and go FOSS.