So that the state actor can listen on the edge of the network and infer with whom you are taking and when? Or maximize their chances of finding a 0-day in the client considering that it's the same client that everyone else's using? Or throwing it all away anyways when it's using Apple/Play services for notifications delivery?
I mean, as opposed to using something like XMPP which you can completely use over Tor and never even reveal which server you use/that you use XMPP, from a client running a secure and minimalistic OS and no service-in-the-middle ?
Some would label Signal as a honeypot and it would be difficult to falsify that.