Not your point, but federation is often heralded as some must-have feature for communication around here, but we already have that: XMPP does that, even with encryption. Or Email with PGP. Or even the old Textsecure code, as Signal/Textsecure started out federated, but, surprise, that didn't help adoption.

This is an explicit design decision. It used to federate, and they found that to be terrible, so they stopped, and now it's better.

Maybe you should find something else to fight against.

https://signal.org/blog/the-ecosystem-is-moving/

Worth noting: Google Talk used to federate, via XMPP. They found that almost nobody actually used the federation functionality, and something like 99%+ of the federation traffic was inbound spam.

Federated protocols aren't very good, and don't evolve.

It already is.

They are; they let the user maintain their own list of phone numbers for their contacts, precisely like the phone company in your example.

> They require the phone number as an anti-spam/moderation measure and hide behind privacy.

This is (inaccurate) speculation from ignorance. Signal, unlike almost every other phone-number-using-service on the planet, does not block burner/disposable/voip numbers from being used with the service.