Well maybe they decided you weren't a good match for the ad after they trawled through all your email.
Adblock, do not track, ghostery, privacy badger, and Google's opt-out cookie are among the tools I'm aware of which may affect this behavior. It's complicated.
I didn't get an ad either. With my search order being Github, twitter, photos, linkedin.
I got the same results. The images are quite random.