Comic books, original paperback books (crime/detective stories, westerns, science fiction, etc.), hip-hop,... all intended as disposable entertainment—the commodified, created content of its day.
That doesn't preclude quality from coming out of it eventually - one of my favorite examples is Walter Miller's 'Canticle for Leibowitz' which was reworked from several of his pulp short stories into a single novel. It's a really great book! I think the incentive structure encouraged volume over quality, but quality still did matter. There wasn't the same algorithm-hacking incentive at play, and you still had to get your works past an editor and approved. Those are important distinctions!
that said, as an aside, im a little nonplussed by the inclusion of hiphop as opposed to, say, 'pop' or 'country', music.