From what I heard, Google’s sells ad space via an auction system. They collect information about a viewer then when said viewer watches a video/visits a website, all the ad space on the video/website goes on auction with the viewer’s characteristics attached in real time. Advertisers will look at the viewer characteristics and decide if they want to bid. The winner of the auction gets the ad spot and has their ad shown. All this is of course fully automated and over in just a few milliseconds.

What this means is, advertisers have full control over what ads you get. Ad space goes to the highest bidder. If you have money, you can spam a specific demographic to death with your ads. Google does not in anyway try to protect the quality of life of its users.