I came here to say exactly this. Source: I work in the guts of some of the biggest telecom networks on the planet.
Federation is a problem because none of the standards interop. The closest thing we had was XMPP which became mega-bloatware as time went by and is now just not something anyone wants to implement (and it's becoming less of an issue as most of the players move away from open-ness).
While the technical among us understand the ramifications of these decisions, the silent majority do not. I believe it was Elad Gil who said that services that eschew privacy have historically dominated their more private opponents. Users say they care about privacy but their explicit value systems (what they say versus what they do) says otherwise. The majority of consumers are happy to take iMessage and use it to the extreme and will attribute silent failures to the operators in most cases (which is not necessarily wrong).
True federated identity is the death of the phone network and there are just too many billions of dollars tied up in the world for this to come to pass. A phone number is a ridiculously arbitrary identifier for a person, and yet it works and has worked for quite some time. Logically addressed networks are finally starting to break, and that's a good thing, but the catalyst that will move us away from these systems is one that subsumes existing infrastructure while adding new features. You cannot rip and replace our communications networks (or any infrastructure for that matter) and so the only logical solution is to subsume. It's not easy, but that's how this gets fixed.