So the current belts were designed to allow slow movement but lock under sudden acceleration. Airline seat belts have a different function too. They are not to help you survive a crash (hardly anyone survives a crash), but rather to keep from leaving your seat in turbulence. By contrast, car seat belts really do help you survive a crash. read more
As Quora User rightly points out, the purpose of the belt in an aircraft is entirely different than the purpose of a seat belt in a car. A car's sash belt is to protect you from hitting the steering wheel (or seat in front) in the event of a rapid deceleration. read more
Each belt is good at something different, and each belt has its own set of drawbacks. The automotive style push-button belt is very familiar to infrequent flyers. Most people who are going to get on a plane have been in a car (they probably rode in one to the airport), so familiarity with automotive-style seatbelts can generally be assumed. read more