[blfr]

Evil ad networks only need a handful of cookies to track you. They could probably go without cookies entirely, just by fingerprinting the browser. They have the resources and know-how.

This happens because many webmasters build frankensites by copying and pasting snippets of code to get the functionality they need. Those load a bunch of resources from all over the net and dump a jar of cookies in your lap. It's the same laziness that makes devs set expiration to 9999.

The popouts, or banners, with cookie information are a pointless annoyance, not an encouraging development.

[jfindley]

Not disagreeing with what you say, but browser fingerprinting is a great deal less accurate than cookie-based tracking, so the ad networks would certainly like to retain a cookie on the client machine, if they can.