Bandwidth and storage are miniscule
Audio is about 8Kb/sec with modern codecs, or about 1KB/sec. You wouldn't even notice that traffic on your upstream. Once at Google HQ it would be converted to text and stored as such, and added to the profile of stuff they know about you. You talk about football a lot, so they will show you football related ads. You talk about how you dad is in the hospital and things aren't looking good, it will show you ads for funeral homes.
Not sure why you would believe they don't have incentive to collect everything - even if they don't act on it today since their "AI" capabilities aren't good enough to do it justice, they'd want to store it because someday when it is they'd have years of your historical info to go through to get know you and your family so much better as advertising targets.
This is how they make their money. This is the ONLY way they make their money! Advertising is over 100% of Google's profit - everything else, collectively, operates at a fairly substantial loss.
Biting the hand that feeds IT
