While you aren't wrong about needing end to end encryption, that would not have helped here. What China was after was meta data (who is communicating with who), which is a completely different problem to solve.
Stupidity and banality is a far greater threat than conspiracy.
Clearly, the counter-intel part of the US government effort has been less successful than the surveillance and intelligence gathering effort. But that doesn't mean that the US government wants all those other nations to be able to gather data from these systems. Our government wants nothing more than to be the only national government capable of gathering data from these systems.
Getting them to actually use them is hard, especially when the whole point of the app is to communicate with other people, and literally none of the people they regularly communicate with other than yourself use (or even know about) Signal.