Revisit the "jump stop"

[Jqb12]

I recently found myself in a position of trying to explain to a coach why his player could not leave the ground on one foot with the ball, land simultaneously on both feet, and NOT be allowed a pivot foot after the landing. Other than simply telling him that it's in the rule book, how do we explain WHY this is traveling? I did a half-assed job of trying to explain it. He didn't catch the ball in the air and then land on 2 feet, it was off his dribble.