High mileage means small. Wish it weren’t so, but it is. If you look at Europe, the cars with the best MPG are small - very small.
Compare the 07 Accord and Fusion. They get nearly the same mileage.
My 91 Fox WV got 40+ MPG easily.. in the 80s the Diesel rabbit easily got 50 MPG.... BOTH were far better machines than the Metro or the Festiva, bigger too.
Its not just size, transmission gear ratios, hp to weight ratio, etc all matter in MPG.
I recently traded a 240 HP car that got 30 mpg average. My wife’s car does better than that at 35 mpg. Both are American cars.
I had a Pontiac GrandAm that got good mileage...which was not much of a concern in the 90s.