XMPP is an old protocol. GTalk (google talk) and Whatsapp used it, then extended it, then didn't give back to the community. So here we are...
The problem with alternative protocols and apps and whatnot is that people are reluctant to change and won't try anything new if only 2-3 other people use that protocol/service. I can't even convince my best friends to use Signal, let alone XMPP.