The non-fiction is an angle I'd never considered. Though as a response that I have no reasonable way of checking, don't university presses make a lot of the non-fiction for the academy? As I said, probably wrong, a legitimate question. And the difference I think that we're thinking of is scale of success. You mention Bieber as the scale of success that you are familiar with, but underground success can make you a living in the music industry, and I think it could be able to with publishing if authors weren't being paid like slaves. The without publishers people would still write, and without record labels the music industry survives because art isn't a commercial product that scales. The Odyssey was written before publishing.
Mozart wrote before record labels. The difference is the definitions of success...megahits versus supporting yourself. Consumerism in contrast to satisfaction.