"Why the ads" is not relevant enough to justify spending my time trying to figure it out.

Just block ads and tracking in general and Google in particular. If DuckDuckGo can operate successfully without tracking, Google and their cling-ons can too. Figuring out how and why --- that's their problem, not mine.

Google is mainly an annoyance, kind of like a parasite. If Google shut down tomorrow, any significant loss of functionality could be easily overcome by the end of the day for most people.