They exist, but in limited numbers. The fleet of used cars on the road doesn't represent what used car buyers necessarily want, it just represents what new car buyers wanted in years past. To get a fuel efficient used car today, you have to have convinced a higher income buyer to have bought a new one a few years ago.
This is why fuel economy standards are a good idea -- the entire market doesn't decide what vehicles get built -- only the top ~1/3 of market purchasers decide what manufacturers build.
