Value Impressions Over Everything Else

Marc Goldberg, chief executive of Trust Metrics, an ad safety vendor, said the effort to remove bad actors ignores that many advertisers value impressions over everything else. They would rather not choose and monitor what websites they are appearing on, he said, because they worry they will miss out on potentially lucrative destinations.
— http://www.nytimes.com/2016/12/26/business/media/advertising-online-ads-fake-news-google.html

Advertisers may value impressions over everything else but I'd disagree that missing out on lucrative destinations is the reason to not monitor the website their ads appear on.

It's too complex, time-consuming and very expensive.