Re: This raises the obvious question
stricter controls and emission limits
Stricter control on EGR diesel (as in 2.0 VW engines) means up to 20% higher consumption. In that case, it is because lower NO2 is achieved by reducing the engine efficiency. The mandatory emission fix as a side effect across the USA provided the petrol companies with several percent increase in revenue from diesel sales. So that alone would justify paying the necessary lobby money to get the hatchet job underway.
In general, the more processing you put on the exhaust, the lower the mileage per gallon.
The USA Oil lobby has fought very long and hard against diesel and is continuing to do so. Instead of a 2l diesel engine in USA they have to fit a 3.2l petrol - f.e. Nissan big models (just to be able to drive the car with all the stuff sitting on the exhaust). Instead of a 2.5 (D-Max, Toyota Hi-Lux) you often see 4-6l Petrols (Colorado, Tundra, etc). This is visible even for Petrol-only models. Where 1.0l or 1.3l Petrol such as the Yaris, Micra, etc is sufficient in Europe, the extra emission control results in a 1.5-2.0l being installed.
That will consume petrol in vast quantities regardless of all the tech used to improve fuel economy. This is also why if you trace the money to the clean air acts (especially in their anti-diesel regs) in USA you always end up running into someone related to Big Oil.