Tinode and Snikket should be discussed too. They're server and clients, built upon XMPP and including the many extensions, "XEPs" that an admin would want in order to give their users a modern experience.

I'm trying out another extremely lightweight nostr relay

I'm going to throw this out there not being sure how true it is, but I find it interesting to think about.

XMPP is much more widely used than Matrix if you count WhatsApp (Meta/Facebook). ActivityPub is much more widely used than AT Protocol and nostr combined if you count Threads (Meta/Facebook). So reasons why people aren't talking about XMPP include not wanting to recognize that Meta is hugely influential in this space and that most people don't talk about the underlying protocols of the services and tools they're use at all leaving a self selected group of people looking for alternatives with traction that don't depend on Meta. Outside of WhatsApp, there's not a lot of traction with any particular XMPP implementation. And none of the XMPP implementations have a Discord-ish organization of chat rooms that's popular and familiar right now. Matrix has both right now (although I don't think it will ever be more than a small niche in the mobile messaging space).

I'm fine with using Matrix for what it is. There are programming language communities that have been very helpful for me and a number of Lemmy related communities that have been nice to be a part of.

I'm not sure if you noticed this, but Matrix is newer. And, as Barney Stinson will tell you, "Newer is always hotter".

STD: Shiny Things Disease.

They'll find something newer soon. And, if it uses some loose install method with performance or security concerns but installs with a negligent curl|sh, they'll be all over it.

because it's new