Cars are built for their purpose, designing cars to be super efficient at speeds they're never driven doesn't make any sense. The higher speed efficiency is a

Cars are built for their purpose, designing cars to be super efficient at speeds they're never driven doesn't make any sense. The higher speed efficiency is a trade-off between all the varying speeds the cars are driven and the limitations of physics. They could also produce extremely fuel efficient cars by ignoring the safety laws (even get around them by building trikes that don't have to abide by the laws) but they'd either not be allowed or never bought because they're impractical.