The game is still in development. So right now the team is probably trying to balace out the characters as well as enhancing graphics and fixing glitches.
Perhaps it was felt that Fox was too good with his blaster out (less lag).
OR another option is an idea of stances. Pit can duel wield his bow by taking it apart, Zamus could switch her gun to a whip, and maybe Fox can take out his blaster.
AND maybe crouching is a stance. So some characters like Pikachu, Wario, and Snake crouch in their stance while other characters (Fox, Zamus, and Pit) mix up their standard attacks but keep their free movement.