Today I saw this article online. Granted the information is from 2012, but the article reports the conclusion from an analytical firm that 60% of the apps in the App Store have never been downloaded, even once.
This figure is both astonishing and completely unsurprising.
You might argue that discoverability is a big problem, and that other App Stores that let you see new or recently updated apps easier might not have this problem.
You might also argue that a large portion of these are fart apps or redundant flashlight apps, or other things that you would not expect people to use regardless.
However, in my personal opinion, this points to a more fundamental problem.