Y'know how nice it is to message someone through my XMPP server, never once worrying that our messages will be intercepted? Knowing that they'll go "poof" in a couple of days anyway? That my little server is beneath most notice in the first place?
I never get a message from my dentist, or the city, or some shitstain who bought a thousand-pack of target numbers and a hundred-pack of SIM cards. It's me and my friends. And, like ActivityPub, it's federated; they don't have to be on my server.
XMPP isn't new and shiny. It's mature. It's robust. Those qualities, in most cases, should trump "new and shiny".
It looks and acts like texting.
I do not get why people keep looking for The New Secure Communication Method, especially ones brought to you by Capitalists.