The thing is, even if Google _could_ they aren't incentivized to. They are more incentivized to show the ad-ridden content, because often the websites are using

The thing is, even if Google _could_ they aren't incentivized to. They are more incentivized to show the ad-ridden content, because often the websites are using Google itself to display the ads. In the case described in the linked post, Google potentially benefits twice, financially. Why would they want to reduce their profit by showing the more relevant posts (those that quickly get to the answer)? I don't know though, maybe StackOverflow also uses Google for their ads, but a quick looks suggests they simply have less ads than the results above them in the article's example search.