I believe Google have hit a sweet spot (for them) where they can keep you browsing a specific topic for a long time while still showing you mildly interesting r

I believe Google have hit a sweet spot (for them) where they can keep you browsing a specific topic for a long time while still showing you mildly interesting results. Since the results are consistently on topic, you are shown ads that are interesting to you time and time again, which results in a lot of clicks and a lot of revenue.