While I think that audio recording is not a thing, your economic argument is not complete.
What if only the audio of "high value" targets is recorded. Meaning people who buy a lot of stuff. So it might be worthwhile to only record their sounds. Which will explain why random testing (usually with new/clean phones) is never successful in detecting a recording event.
I think this is a genuine concern for prominent people. Like if you are Mark Zuckerberg, there is material interest in a bad actor installing malware on his laptop. But for a random person where you get low value data that may or may not let you better target some low value ads? That is much harder to justify. Would have to reevaluate as things change and the cost of compute goes down.