Yeah, that does bother me. But it's also a lot easier to build a centralized service like that than to get people on a decentralized one.

If you really want something private and are willing to jump through a few hoops, Simplex exists. But most people aren't willing to jump through a few hoops, and even Signal (a pretty low bar) is a hard enough sell as it is. And that's why I use Signal, because it's my best chance to get people onto something better. In other words, don't let perfect be the enemy of better.