This is a structural problem and anything that gets large enough will succumb to the same forces. If the incentives are for optimizing ad revenue then that's what all corporate machines will do at scale, regardless of their initial motives and incentive structure. It doesn't help that Google is also an ad network, hence the ouroboros aspect.
It's the same with social networks, upvotes and likes skew the the type of content that is generated to be liked by the people liking and upvoting instead of being insightful. Popularity is not the same thing as insight so the social web is full of mostly useless but popular content.
Paul Graham has been pushing for someone to disrupt web search on and off for at least the last 10 years: http://paulgraham.com/ambitious.html
(he tweeted about it more recently, but I couldn't dig it up since I'm not much of a tweet man)