His other example, Snikket, is self hostable and interoperable with the wider xmpp world. The pattern is largely related to companies wanting to build walled gardens. On that basis, most open source tech has "failed" in the sense of having created greater value in VC backed companies with marketing departments than in communities without them. It isn't really surprising that it works that way, and IMHO it isn't failure.
That's really the key and the end of it - SMTP was big enough that all the companies had to work with it, even the ones that originally wanted to walled garden (Lotus Notes and Microsoft Exchange are two big names, even now Exchange still has X500 stuff in there).
The closest thing to that which chat has is text messaging, and I'm honestly surprised that MORE platforms don't have a text messaging "bridge" of sorts.