The car crash data confirms this too. I thought of the egg drop experiment when thinking of "crumple zones" which does make sense. To protect an egg from a drop you want the outer layer to contort and crumple which decelerates the egg more slowly vs a hard rigid structure which will transfer force to the egg much more abruptly. I'm no physics guru but that is what I came up with that makes sense. Unibody has crumple zones which decelerate the passengers better than body on frame.