I'm not an advertiser and I understand your point - but I think it can be the same amount of work pushing the ad in a black hole of ad impressions - not knowing where your add is being displayed - just some numbers - then trying to guess - because it's a great amount of guessing involved - what should you do to increase the relevance of your ad.

Vetting the apps you want to advertise can also mean time spent - but knowing what are the apps where you are displaying your apps and even who are the type of users being the ad - I for one feel this is a more powerful approach.

But yet again - I'm not a big advertiser spending huge money on it.