Part of it might be that musicians and composers have a finite boredom threshold. As a jazz musician, much as I love "the girl from Ipanema," and it's one of the greatest songs ever written, if I have to play it yet again in the same way as it's always played, I find it hard to refrain from misbehaving.

I prefer playing music that is more avant garde (within my abilities of course) even if it appeals to a smaller audience.