Because petrol is cheap here, $3.00 to $8.00 in the UK. Now if you were a diplomat you could have one.
If you can somehow manage to live in the UK for a while, and drive a Jeep while you are there, you may be able to import the vehicle to the states. A friend got a Volvo in Sweden, drove it for a few thousand miles, and saved quite a bit importing it as a used vehicle. That was a U.S. compliant vehicle though.
The bottom line is that "they" don't want you to have this vehicle, the fuel for the gasoline vehicle is still cheap enough, and given all that the cost to market it in this country is prohibitive.
Cheers,
Earle