It's nothing to do with Google advertising. It was a problem before Google had advertising. Being the number 1 non-ad result for a search will get you many more

It's nothing to do with Google advertising. It was a problem before Google had advertising. Being the number 1 non-ad result for a search will get you many more hits than being a number 2. If you don't appear on the first page, you may as well not exist. Google's priority with ads is to make sure ad buyers are happy with the results they are getting. This means making sure the people who click the ads go on to buy the product being advertised. That's what ad buyers measure.