This isn't a consumer car situation. They're not trying to hit some paper efficiency number that matters environmentally in aggregate but is hard for any individual with highly variable driving, pricing etc to really notice. As the article also emphasizes this is about cold hard money in real world constant heavy usage across the entire country since this is long haul. These vehicles are going over 100k miles a year, which at their fuel economy translates to something like 14000-16000 gallons of diesel per year, and in turn at an average price of ~$4/gallon [0] is like $50k-60k, per year, just in fuel. Individual truckers and companies will absolutely notice whether they're adding 5000 to 6000 dollars to their net income per vehicle, or not.

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0: https://www.eia.gov/petroleum/gasdiesel/

If you had a VW TDI, you got better real world fuel efficiency than the EPA fuel efficiency. And lower CO2 emissions. And all you had to do was wiggle the steering wheel ever.

Yes, yes, some fraud. Yes, yes, NOx emissions. But the fuel efficiency numbers were better than published.