Google doesn't just live in a single client. As a user (by giving up my privacyto Google), I can ask my Google home how my day is while getting ready for work. I can see the status of my flight tomorrow in my Google app (or Google home screen in Android) without a single search - just because it parsed my email with itinerary. Same way, I can see status for my FedEx package right there just because they violeted my privacy and scraped when I purchased something.
Imagine how much friction it'd require to setup such devices if everything was processed on client side or required explicit opt-in before accessing the info.
Of course as a side effect, I get advertisements of standing desk even a month after buying one, but probably the alternative would be to pay for all these AI and assist?
Again, just a user's perspective.