[Closed] A question about ads & cookies

I bought some new sunglasses the other day. I'd looked at them before and even went as far as clicking 'buy' just to check that there weren't any weird delivery costs at the checkout. So I wasn't surprised that the adverts for them followed me around.

The thing is, now I've bought them I'm still getting them advertised to me. Same glasses, same seller. I've had similar before with other stuff.

So my question is, if there's a cookie to say 'this guy wants sunglasses, show him sunglesses', why isn't there one that says 'this guy bought the sunglasses, show him something else'?