Because keeping diesel cars away from the US market leaves them with a bit less competition. American companies make some diesel cars in other markets (Ford, a

Because keeping diesel cars away from the US market leaves them with a bit less competition. American companies make some diesel cars in other markets (Ford, and GM with its Opel and Vauxhall brands) but they have a significantly smaller market share in diesels than in gasoline engines. Easiest way to look at it is this: http://www.statista.com/statistics/425324/eu-car-sales-share-of-diesel-engines-by-brand/ http://www.statista.com/statistics/425324/eu-car-sales-share... You'll find Opel, Vauxhall and Ford towards the lower end of the table.