

It’s a crapload more work to support XMPP/Matrix/whatever messaging on any platform than just using a robust, reliable, resilient, widely supported good old SMTP
For the minimal of sending out a message to their accounts, they are just as easy as each other. Heck, there are simple packages to send XMPP messages from the CLI.

[citation needed]
There’s at least three good clients for Desktop (multiplatform) and two for Android.
Plus, XMPP is the best thing to run service-wise. Relatively cheap, runs on a potato, not a nu-protocol that requires a server cluster and friggin’ npm.