The 14 year olds on Reddit have really been struggling with this fact
1,439 karma · joined November 13, 2012
Search ads give companies a legitimate way to promote apps within the app store, outside of editorial or bad tactics to game search results (title keyword stuffing, keyword highjacking etc).
The App Store is where the customers are, so it makes sense to allow advertising here. Otherwise the alternative Google or Facebook where you're changes of conversion are such a great deal less because you're so far removed from the channel.
It's like the difference between being offered fries at the fast food counter compared to a banner ad. It's clear it's going to be better for all involved to be offered something in the better context.