It's strange how you think the latter options are the pretty obvious explanations. "Google wants to spy on you with hidden mic" seems to be the fairly obvious one to me.
What's strange is the amount of pro-government and pro-google comments on hacker news the past few years. I wonder what the two options for why that is?
Also, you are offering a false dichotomy. This isn't an either-or situation. There could be other reasons. Could be that "google wants to spy on you with a hidden mic AND they planned it for the future". Another option is "The mic was put there by mistake". Another is that "the supplier screwed up". Or another is that the "supplier intentionally put it there".