Also, as a publisher who provides educational content (I'm not mentioning my website's name, but it's very, very similar to mentalfloss.com or the TIL reddit subreddit [even though my website has been around longer than both]), increasing the top ads is going to hurt my traffic. It's a bit of a selfish reason but at least I know the people who are searching for those terms are looking for exactly what's on my website. In many cases, my site is the only one with that information.