My guess they're setting ad preferences cookies for certain ad networks that are then used by various sites as pay-per-click revenue for the hosting sites. So w

My guess they're setting ad preferences cookies for certain ad networks that are then used by various sites as pay-per-click revenue for the hosting sites. So when you'd see an ad served from Google's* ad network or Outbrain* or someone, it's as if the target had told those ad networks what kind of advertising interests them more than others. * These are named as examples of ad networks and I don't mean to imply they are used in this scheme and definitely not that they would be complicit or cooperative with it.