Signal is an improvement over twitter or facebook mesenger. There is no way I would be able get my friend group to switch from those to XMPP but I did get then to at least switch to signal. Is it a perfect solution? No. But it's a hell of a lot better than what came before. Eventually I might get them over to something better like XMPP but nontechnically inclined people can't make that jump in one go.

Looking at this as someone familiar to FOSS is a completely different perspective than for the average person. If you tell the average person to use XMPP then they're going to type XMPP into their preinstalled app store and get confused about "which app is the XMPP app".