Brand awareness campaigns and media buys would be the sort of exception you're talking about and you're absolutely right. Or if you're a company who buys a ton

Brand awareness campaigns and media buys would be the sort of exception you're talking about and you're absolutely right. Or if you're a company who buys a ton of fraudulent traffic in order to inflate your Alexa/Quantcast/Hitwise/etc rankings, then every impression counts as well. However, if the advertiser is like the bulk of online advertising (e.g. one of the many for-profit online-degree-mills or someone pushing the latest weight loss pills) they tend to very aggressively optimize towards a desired CPA and eliminating non-converting traffic is always the goal. A better CVR creates happier advertisers which leads to higher bids & budgets and then higher publisher payouts.