https://marco.org/2008/01/04/google-added-those-left-right-arrow-buttons-in-the
Google added those left/right-arrow buttons in the ad boxes. That way, if you want to see more awful AdSense ads, you can just scroll through them all with slide and fade effects!
Someone at Google had a bit too much of the punch at the holiday party. They’re under the delusion that people want to see ads. This is a common delusion among publishers.