It’s actually about raising the price for advertisers: Instead of only political books being able to advertise on that page, they’re bidding against beef jerky

It’s actually about raising the price for advertisers: Instead of only political books being able to advertise on that page, they’re bidding against beef jerky and cars and so on. This raises the price for the ad slot by creating (false) demand. Without those out-of-place, targeted ads there would be less demand for every ad slot, and people could bid less for them.