Why not
Why can't they have a policy where a cookie can only be SET if it's from the first-party website, but is USED even in third-party. That is prevent a third-party site from setting a cookie.
Basically, I'm never going to visit the ad broker's website directly, so they can never set a cookie to track me.
Combine that with a forced expiration within a relatively short time (eg 30 days) just in case I get one and don't clear the cookies myself.
Apply the same policy to local-storage etc
.
What am I overlooking? Sure, google won't have a problem with setting a cookie, but they have so many avenues of tracking that it's essentially irrelevant. The other networks can all FOAD