It's really hard to quickly replace millions of vehicles.
It easily takes 11kwh to charge a Volt. It'll go about 35 miles in the summer on that charge, and more like 28 in the winter.
It also gets 35 mpg on gasoline, while providing free heat in the winter from the gas engine heat, and for most of the last few years was doing this for $3.50-$4 a gallon.
There are people on Southern California/San Diego that pay more. Over there people say the Prius Prime is WAY cheaper to operate on gas because it gets 50mpg gasoline.
I've even heard people running their home off gasoline because it's cheaper but that would require an impressive gas generator to do long term.
If my maths is correct, we are paying US$6.10 a gallon here in NZ.