I think part of it is that XMPP dates back to the late 90s, when we thought XML was a good thing (not realising that it is, in fact, a kind of information techn

I think part of it is that XMPP dates back to the late 90s, when we thought XML was a good thing (not realising that it is, in fact, a kind of information technology antimatter, which annihilates anything it touches, leaving nothing but bugs and hurt feelings behind). The protocol in action feels crufty, and the massive number of optional extensions means that you're never quite certain if your client, your server, your correspondent's server and your correspondent's client will all play ball. Then you toss in the fact that all the big players have decided that walled gardens are just awesome, and the fact that no-one today would touch anything using XML with a 1,024-foot pole — and thus there's just no ecosystem for it anymore. (as an aside, I believe that in a century our children will consider the digression to XML & JavaScript to be as inexplicable as we do China's decision to scuttle its fleet of exploration)