There's a long and complicated answer to that question. But the simple version is that, for a variety of reasons, the US auto industry and govt decided (for a variety of good and bad reasons) to favor gasoline over diesel, resulting in a higher tax on diesel fuel than on gasoline. Now the infrastructure is entrenched and it will cost mucho bucks if folks re-adopt diesel suddenly en masse. But there has been a growing interest in diesel fuel amongst US consumers.
I personally support a significantly lower tax on diesel fuels as a way to help speed the adoption of diesel vehicles in America.
Oh I understand the reasons but even with the higher taxes on Diesel a 65mpg car burning $3.59 a gallon diesel is much better than a 30mpg car burning $3.27 a gallon gasoline. Plus when you factor in that algae based biodiesel is a very possible future alternative to fuel (or at the very least a supplement to standard diesel) it makes even more sense for the future.
Electric cars I think are a boondoggle. Who wants a coal burning car?