> Google has an incentive to rank pages that contain Google ads because it makes them more revenue. Google has an incentive to rank profit-making sites higher so that they make more money.
They don't have to intentionally rank them higher, but this fact could prevent them from choosing to rank ad-filled sites lower even though it would do wonders for search result quality because ad quantity is usually a good proxy for spamminess and trash.
Is there evidence that they do this?