"XMPP support is slowly but surely being removed (just imagine a phone system where every number you call to may require a different telephone)"
So what happens in these kinds of cases is that somebody invents an abstraction (a metaprotocol) that cross-connects all of these. And then somebody comes up with yet another protocol that doesn't fit into the metaprotocol (or some slow moving standards body can't fit the new one in), so somebody else comes up with a metametaprotocol that bundles the metaprotocol and the new one in....and its abstractions all the way up..
Until somebody realizes that the tower of abstraction is introducing 300ms of lag into things and we all pine away for the good old days of just XMPP or whatever.
There's nothing that prevents technically oriented people from setting up ftp, nntp, smtp, mtp, etc. servers and so on except that these things really tend to rely on some kind of software running on the user's OS and these days people pretty much just run a browser and not much else.
The answer then is move the functions those protocols supported into the browser (like in the way that most browsers support ftp), but it's just not worth trying to shove telnet or whatever into browser support, so people just replicate whatever telnet is supposed to do into a web app that's access over http.
I think more troubling though is non-browser server-server communication is now just http. Sure it's pretty simple, but for server-to-server communication there's almost always a better protocol to use, but people can't be bothered to come up with one.