Why would Google be recording your mic and using it for ads where they would just be caught for doing it? I mean it's completely possible. But more likely just confirmation bias. Speaking of Occam's razor, we should just dump modern "technology" (smart phones, smart TVs, the web, IoT, even feature phones were no good).

There's actually nothing hard about the concept of a mobile phone, it's just a computer (or could even be a simple PCB) with a mic and speaker. No need for "secret sauce" standards such that nobody can tell if it's secure (I mean it isn't, the bugs just get patched every week, day, nanosecond, whatever). Hell, you can even make a completely open and simple (even more important than open) phone communication standard and charge 1 billion people tens of dollars per month to use your network and become the richest person on earth.

edit: I mean facebook, or whatever (also facebook would have to gain access to the mic [maybe facebook has mic permission i guess, i am unfamiliar with smart phones])