Well, I’ll chime in that my old Honda CRX (2-seater) got 65 mpg highway (or better) back in the days of 55 mph. It got around 48 mpg overall. No, it’s not a family car, but it was great for me as a single guy back then. It was actually quite a comfortable car for long trips, and I hauled some fairly amazing stuff around in it, for such a small / eficient vehicle. ‘80’s technology, too...
Your CRX weighed less than half of what the current smallest car (save the Smart) does.
All those mandated safety requirements and gear add weight to the car. Airbags alone add about 500lbs to the structure of a car.
Weight is the enemy of fuel economy.
Your CRX is illegal to manufacture and sell today.
The proof is in the past! They MADE the cars with great gas mileage so why not now? Why not here in the U.S.?