Personally with XMPP, I think it’s right now because of the lack of decent looking clients (especially on iOS), as well as a lot of the same friction that people have suffered with mastodon.

Also, Signal is built towards a completely different audience that places privacy first over modern messaging features (things like API’s, sending messages through voice assistants, etc.). And for SimpleX, I’m not really sure if sharing a QR code/link with someone else is the best route to go in UX just to message a friend