It's a game of averages - what you're doing is watching a blackjack game and saying "why on earth didn't you double down on that 18, the next card was a 3!"
Sure there's a lot of errors in advert targeting, but they don't need 100% accuracy to see results, and on a scale from "just chuck adverts at everyone, some will be relevant" to "let's have people manually look into every user to profile them and know exactly what to target them with" there has to be a point where it's not cost-effective to make things even more accurate.
Sure there's a lot of errors in advert targeting, but they don't need 100% accuracy to see results, and on a scale from "just chuck adverts at everyone, some will be relevant" to "let's have people manually look into every user to profile them and know exactly what to target them with" there has to be a point where it's not cost-effective to make things even more accurate.