I think it's because (1) most really good music-oriented speakers are designed to run without subs, and (2) most subs are designed to make the floor shake when watching movies with overdone explosions, or to one-note "music".
Good-sounding music-oriented subs (Rel, Vandersteen, et al.) exist, but they're the exceptions.
Good-sounding music-oriented subs (Rel, Vandersteen, et al.) exist, but they're the exceptions.