Yup, and that’s why monopolies are bad. Once you get a dominant position, the way to increase profits is by abusing your market position. And publicly traded companies need to increase profits because that’s what shareholders expect.

In this case, reducing the quality of search means people need to search more often, which means they see more ads. As a double-whammy, if you improve the relevance of the ad results while reducing the relevance of the regular results, you get more click-through on the ads. So Google has little incentive, while it has a dominant position, of having a good search product. They’ll only care again if that dominance gets threatened.