Because there's a negative perception hump to get past in the usa. I tried suggesting a diesel, and everyone complains about how dirty it is and other myths.
There are diesels that get even better millage, like the Audi A2 with a mileage on it's diesel model ranging from 80 to 120 mpg. I never understand why car manufacturers don't make aerodynamic body designs for their cars. A honda insight with a diesel engine gets similar mileage.
It used to be difficult - to the point of being impractical - to make a small diesel car run cleanly. IIRC, the technology really only arrived about 5 years ago. Also, large trucks belching plumes of black soot were pretty common until recently, and this is how many people here still think of diesel.
There are diesels that get even better millage, like the Audi A2 with a mileage on it's diesel model ranging from 80 to 120 mpg. I never understand why car manufacturers don't make aerodynamic body designs for their cars. A honda insight with a diesel engine gets similar mileage.