Where I live we have laws in place that criminalize stalking. Why isn't this considered stalking?
Maybe you implicitly agree to their ToS when you enter a partner store? It's a technical detail of creative lawyering. They must have covered the legal aspects and factored in the fines in case they get a slap on the wrist. I guess it is the same thin line you have between tax evasion and tax optimization and Google has a nearly unlimited budget to try to move this line in their favor.
I know that I sound dramatic, but all of these kind of things that we have let Google do would be considered HIGHLY illegal if instead of a company it was a single, private individual.