If musicians read sheet music like programmers read code, then why do a lot of programmers insist that everyone else comments their code?
If you're reading sheet music just to play it, then you wouldn't need comments (like a computer doesn't need comments to execute code). I would be surprised if music composition is done exclusively in notation without some text alongside it, particularly if there are a number of composers collaborating (disclaimer: I'm not a composer).
If people could write perfect software first time (and software requirements never changed), code probably wouldn't need comments.