It's zero sum for the advertisers - for each ad spot, there can only be one ad, so if I win the auction, you lose. Of course, since it's an auction, the winner

It's zero sum for the advertisers - for each ad spot, there can only be one ad, so if I win the auction, you lose. Of course, since it's an auction, the winner will be spending increasing amounts of money on it, with no real upside (still the same amount of ads displayed). It's all very good money for the ad platform/brokers.