"Before you assume that ads that aren't clicked on are wasted, have a bit of a read up on things like
https://en.wikipedia.org/wiki/Mere-exposure_effect"
And before you assume that they aren't wasted consider the possibility that the effect might be negative.
"Car adverts are a good example"
Indeed. A very good example. I bought a new car a couple of years ago. Within a very few weeks I started getting texts and marketing calls from the dealer (or at least from the dealer's marketing agency). Did they think the brand new car they'd sold me was such crap that i was going to go out & replace it? And if it was did they think it wouldn't have been a claim under warranty backed up by solicitor's letters? Despite telling the callers to stop it continued. It only stopped when I got hold of the MD's email address and informed him in no uncertain terms that although they'd get the servicing for the remainder of the warranty they'd get no further business from me ever because of their pestering.
Mere exposure certainly works but not as intended.