These days, the mainstream music scene produces catchy, pop songs or one-hit wonders that span for just a few months. Afterwards, most people normally just cringe when they hear it again, and decide to go back to their favorite classics or artists. That is why, in a way, popstars earn more. They have release songs more frequently to offer something new and build up their images.
Given these, more music enthusiasts still download their songs, but not their albums. Pretty soon, they would want to just delete them for a “Clean Up iTunes” approach. Artists that they really like are retained for their music collection.