It’s probably some inertia thing, but that shouldn’t prevent us from being able to land safely, should it?
The same thing that prevents you from safely landing after being shot out of a cannon. Jumping out of a moving car means you’re moving at the same speed as the car when you jump out. Human bodies aren’t designed to move at car speeds, but you need to get rid of that extra speed somehow, which in this case involves your bones breaking and your skin being cut up to get rid of that excess energy.
When you jump out of the car, you’re traveling the same speed the car was. And you don’t slow down meaningfully on your way down, so you touch the ground at very high speed.
The ground, typically, is hard, rough, and full of pointy sharp objects, all of which you hit at whatever the speed of your car was. That creates more than enough friction to rip your skin off, and the uneven force on your body can send you tumbling with enough force to break your bones and cause massive internal injury.
If you exit a car going 70mph, you would be moving at 70mph and the only thing slowing you down is the ground
It actually is possible. You just need to be wearing full motorcycle gear and then roll properly. And then you risk the injuries a motorcyclist gets in a crash.
It’s because you are going the same speed as the car you are in. This means that you have a lot of momentum. But, unlike a car, you do not have any brakes.