Because cars aren’t people. We sacrifice the car to keep the person as intact as possible, which means having crumple zones and specially designed structural members that direct energy away from the passengers.
For a person falling in an elevator, standing allows you to sacrifice your legs to keep your head as intact as possible. Laying down means your head is in direct contact with a very hard surface that is going to smash the shit out of it when you hit bottom.
Who are you calling a shithead?
That’s what’s making me think you have to specifically design for energy absorption, you can’t assume the part closest to the impact will absorb the energy. Also, legs are designed to bear load along their length, making them more like the “safety cage” than “crumple zone”.
If I’m driving a VW Microbus/Kombi, or Vanagon, forget it. My legs’d be gone.
Unless you have a perfectly rigid material, something that doesn’t exist, there will be some energy absorption. In the case of a really old car it will be very poor energy absorption and you’ll lose your legs, but in the case of a crashing elevator or a high jump onto a hard surface it will be significant and you’ll lose your legs.
The losing your legs part shows us the situations are equivalent.