Why can't pass interference be called on a punt fake?

Answer 1

No because a punt is not a pass.

There can, however, be fair catch interference. Whether the receiving player calls for a fair catch or not, the kicking team has to give the receiver an opportunity to field the ball.

Answer 2

Pass interference CAN be called on a fake punt, however the outside players in the "gunner" position cannot be interfered with. On any given punt play, those players are blocked by up to two players on the punt return team, and as such, any punt play in which the punter tossed it up to one of his gunners would result in an interference call. These players can draw penalties for holding against the punt return team, and interference is NOT allowed against other members of the punt unit.