I wonder if the culprit is AdChoices?
While Google often shows you ads based on the content of the page you are viewing, we also show some ads based on the types of websites you visit, view, or where you interact with an ad or other Google product supported by Google's advertising services. In doing this, Google doesn't know your name or any other personal information about you. Google simply recognizes the number stored in your browser on the DoubleClick cookie, and shows ads related to the interest and inferred demographic categories associated with that cookie. It's our goal to make these ads as relevant and useful as possible for you. Google doesn't create categories, or show ads, based on sensitive topics such as race, religion, sexual orientation, or health.
I just stumbled on it. I am surpised I haven't heard about it before and that it is not more controversial.