The Signal team essentially invented the cryptographic constructions the current wave of (good) secure messengers are based on, work for which they were awarded the Levchin Prize at RWC (for perspective, this year's winner was Hugo Krawczyk). They did the work, then published it, for the other messaging systems to adopt --- which is why you can easily get a comparable, though inferior, version of Signal's cryptography in a messenger that doesn't require phone numbers.

At some point in the future maybe the roles will reverse there, and interoperability will be a bigger issue. For now, I think Signal's userbase is benefiting from the decision. If it became necessary, presumably they can alter their stance in the future.