I’m getting 30-38 MPG ( real mileage ) in a 2006 Honda Civic and it’s not a hybrid.
I don't understand this nonsense about not being able to come up with fuel efficient cars. The 1989 Geo Metro got well over 35 mpg, in fact some models were up to 75 mpg.
Now as to whether or not very many people would want them, that is another matter. Chevy / Suzuki someone, make a better built Geo. It just might sell.