I see this from two different angles.
One, the rear seats don’t have the same frontal airbags that front seats have.
Two, on the other hand… I’ve had a LOT of passengers neglect putting on seat belts in the rear as they cite (outdated) laws or whatever not requiring using the seat belts in the rear. Outdated because much older cars only had lap belts which were more likely to cripple people in “less than life threatening” accidents. But modern cars have shoulder straps for rear seat belts too, so there’s no reason to NOT have the seat belt on.
Similar to outdated belt laws, more and more modern cars are designed to avoid having intrusions into the cabin. When you have an intrusion, then front seat occupants can get injured (like having the steering column crush the driver’s legs). But until there’s an intrusion, the whole cabin acts as one contained space… which means impacts and whatever affect front and rear occupants the same way. And this now goes back to the first point, without a frontal airbag for the rear occupants, they can either smash into the back of the seat ahead of them or get whiplash… assuming they’re far enough and have their seat belts on.
