The market is full of fraud, and the surveillance exists as a counter to the fraud. Users are surveilled in an effort to prove that they are real users, not bots that are being used to fake impressions or clickthroughs. It's all very messy.
Place yourself in the shoes of an ad buyer: a random website offers to display your ad. How do you know what you're getting?
Place yourself in the shoes of an ad buyer: a random website offers to display your ad. How do you know what you're getting?