I'm not sure if it's a law everywhere or not. I think it should be. It's not just the person in the car that it affects. If someone's car goes out of control, and they are thrown from the driver's seat by the spinning force, now they have NO chance of controlling their car. Their car is now a gigantic missile about to crash into many innocent other people. So to say "A driver should remain in front of their steering wheel" seems pretty reasonable to me!!
Seat belts help in crashes to protect the driver from going into the windshield or out of the car - but they ALSO help in accidents to keep the driver squarely in front of the steering wheel and pedals. And many, many times that's the difference between the car staying in control vs the car crashing into others.