I think people don't like to think themselves as a product, but that's what we are. We're a potential source of income, and companies will want to know how's your health, where do you go, what do you buy, how you use your time, etc., in order to realize as much of that income as possible.

It's a mutually-beneficial trade-off, it's just that one party gains individually, and the other gains by quantity. Advertisers wouldn't care a lot what restaurants you like, but they care a lot about what restaurants people in your city like.