In Germany it is not just about the efficiency: diesel fuel is taxed lower per liter than gasoline, for exactly the same stupid reasons personal cars are (were?) often cheaper to register in the USA if you find an excuse to call it a truck.
It's a vicious circle because owner of diesel cars may think twice before voting if a candidate proposes to raise the taxes on diesel, even if year after year we get reports about the number of early deaths because of fine particles…