AdSense uses a sealed-bid auction system with arbitrary number of lots that Google controls. It's a FOMO market driven by artificial scarcity, and since Google contractually forbids AdSense-enabled websites from using competing services, it forces ad buyers to go through their closed, controlled system.

But in practice, nobody (well, nobody making lots of ad revenue from their website) uses AdSense exclusively. Most don't even use it at all - AdX is better as a header bidding fallback than AdSense. But those who do use AdSense as a fallback are using it in competition with many other ad networks.

They forbid those websites from using competitors? Isn’t that blatantly illegal? I guess it’s not actually illegal until they lose a court case for antitrust.