As is clear by now, the only way for ad networks to provide any sort of extra value to the service is by choosing the exact image very carefully. To choose the ad carefully, the person browsed must somehow be differentiated, and there really isn't anything to do but tracking.
So ad networks must by logical necessity turn into unregulated surveillance networks and try to soak up as much data about every visitor, collect and collate this data for the express purpose of tracking individual behaviour and then use this information to choose the image.
This creation of a private surveillance network for tracking of individuals is basically the minimum level of sinister an ad network needs to have any sort of "dynamic" product. Yet, at the end of the day, banner ads don't amount to more than very basic content, so it hardly seems justified to create an invasive surveillance apparatus just to serve slightly less irrelevant content.
And there doesn't seem to be much at the other end of sophistication: paid sub sites with dynamic recommendations for the visitor based on stated preferences.
Banner ads can never amount to more than those small ads crammed into the edges of the newspaper, despite being in a domain where companies can talk to users directly and dynamically. The reason for this is that you don't have a conversation with someone trough a small hole in a newspaper and as long as that is how you serve your ads, spying on the user is the best you can do.