Having worked at large companies before, I'm almost certain that more than one person working on the product raised the point "this has a microphone, why isn't it documented?" or "this has privacy implications", but was silenced. (Or it could be that everyone working at Google has been carefully chosen to not have such concerns; I do get that feeling sometimes too.)
So while I agree with you, it _also_ wouldn't surprise me if someone raised the concern, but that person was on a different / more silo'ed team and therefore the concern never reached the execution stage. Herego too many management layers and/or nodes of entropy for communication.
But that's just a hypothesis.