OK, so I’m a conspiracy theorist here, but if you where a Goliath like Google with almost absolute power over search, could you stop yourself from becoming even a smidgen corrupt?
This is a factor that I think may be tested regularly, or even left in place, to improve the CTR percentage balance of paid ad placements.
In other words, I suspect that the Great Goog might purposefully dabble in making some of the organic page 1 search result placements not as favorable for users as absolutely possible, in a hope to bias more people to choosing paid ads.
What can you do about this? Nothing. Can’t prove it either.