Advertisers are sold the idea that 1000 clicks/impression is X dollars. The average impression might be priced at 1000/X$.
But you are worth much more than that for two reasons.
- you are a person willing to pay 5$
- Google can sell a “collectivized” product. The same way that eg collective farmer crop insurance creates actual value.
and the third reason (as consequence of the second) they dont want people to think about: it gives them more opportunity to fudge the value by making it all very complicated.