Makes all the sense in the world and would save billions of dollara but it will not happen because changing it would initially cost a multiple of the savings and hence pay off at the earliest a decade later. Unfortunately American style capitalism cares only about the short term and hence the motivation is not gonna be there to change.
The USA was abuzz about it in the late 1970s, and I recall it failing when Time magazine published an article about the difference between a gallon of gas and 4 liters of gas. At that point I believe the public wanted nothing to do with it in their daily lives, since they were not willing to make such a mentally-draining adjustment. Because average Americans have the intellectual abilities of a bean bag.