Maybe, but I'll suggest an alternative view that's probably unpopular: big ad companies walk a fine line between what knowledge they can share even from _inside

Maybe, but I'll suggest an alternative view that's probably unpopular: big ad companies walk a fine line between what knowledge they can share even from _inside_ the same company. Ad sellers cannot have perfect information for probably several reasons: auditing, privacy, safety, and legal. Evidence of this is that ads are reported as being encrypted between business units (e.g. if you work on ranking product listings, you may no idea what ad is injected at the top). Obviously the result looks stupid to us as consumers which is quite memorable. I suggest it is a by-product of intentional choices. IMO this is a better explanation than "oh this company is just too stupid to do it right, but also they are all knowing about everything you do and are just so doggone evil." Maybe they are that evil, but I am sure they have learned how not to overturn their apple cart and this is an obvious result of that.