It's a bit fuzzier, sure, but listener attention is not an unbounded resource. Neither are radio play, space on movie and TV soundtracks, slots on Pandora playlists, and so forth. If you become a popular musician, your work's going to be funging against something, and most of that something is probably going to be other musicians' work.

(The rest probably comes out of people's attention budgets more generally, which isn't as narrowly competitive but is no less finite.)