Dave Grohl has been all over the place doing press for the Sound City Movie and I'm glad this question came up: Why won't the Foo Fighters play Nirvana songs?
He was pretty straight forward in the answer he gave to tchadquarterly.com:
"You know, that’s hallowed ground. We have to be careful. We have to tread lightly. We have talked about it before, but the opportunity hasn’t really come up, or it just hasn’t felt right.”
Dave also explained that he and Krist Novoselic won't let Nirvana songs be used in commercials and rarely in other things because they are special and need to be kept that way.
A short interview but very cool of Dave to take a stand like that. Click here and read the whole thing from tchadquarterly.com.