Comment by marginalia_nu

> The incentives of ad-driven search engines are to keep the visitors on the search engine rather than direct them to the source.

It's more complicated than that. Google's incentives are to keep the visitors on the search engine only if the search result doesn't have Google ads. Though it's ultimately self-defeating I think, and the reason for their decline in perceived quality. If you go back to the backrub whitepaper from 1998, you'll find Brin and Page outlining this exact perverse incentive as the reason why their competitors sucked.