Because Meredith Whittaker likes it out of jail. True privacy messenger can not have a company behind it, just the open source code. And not require a phone number. I never used Signal, went straight to SimpleX.
Discussion
Indeed. Having a company behind it is a central point of failure. It should be pure math and code.
I will look into SimpleX.
Still I find bending the knee at the first signs of resistance a sign of weak character. Perhaps disbanding the company behind Signal and distributing the source code everywhere would be the better answer.