First let me state upfront I'm not arguing against clean air regulation. I am against the method used to supposedly achieve it, not the objective. The reasons that the main manufacturers don't build Diesel-Electric (Exception being VW and Mercedes and their straight Diesels) for the US market, comes down to the following.
1. Emissions: Diesels, as sold in Europe, and non vehicle applications, as of yet, don't pass the emissions standards, especially for particulate, and NO2 emissions.
2. Perception: Americans tend to rely more on what they think they have heard than investigating for facts. When they think of Diesels they think of the smoke belching, trains and buses around the city and the "sounds like it's about to fall apart" rattle of diesel pickups. Diesel engines that are clean and quiet (like VW or Mercedes) don't get noticed. In fact rarely do people even know that they are a diesel.
3. Patent problems: Diesel Electric is the primary mover and shaker behind trains. Has been for decades. They hold the patents on the easy solutions and this presents a problem for development in the US. US manufacturer's love to hold patents.
4. EPA testing methodology,and laws: They are designed for gasoline vehicles. The cost, which industry would bear, to create new regulations and to motivate legislators and bureaucrats to change them is extremely high in the US. Unless you give the vehicle only 3 wheels. Then it gets much cheaper.
Side note, building the vehicle these gentlemen have built would likely be impossible in California. Emissions laws here largely prohibit installing an engine not of the same vintage or type as supplied by the original manufacturer. It's a sticky gray area that could make it very difficult to get the vehicle licensed if you run into the wrong gov official. 5 years ago I had to give up (as in donate to a cause) a nice little car I owned when I moved to CA because, even thought the car was equipped with the full CA emissions package, and could pass smog, it might have been run on gasoline not compliant with CA standards. (Direct quote from what the DMV told me) the cost to remove the CA emissions package and re-install it and get it "certified" was more than the bluebook on the car, so I had to dispose of it. (I couldn't sell it in the state.) So when you ask "Why doesn't the US have...." it's because the law dictates methodology not standards. IMHO.