The NOx specs weren't impossible to meet; VW cheated to save money and improve performance.
It didn't work. How could they be so stupid to assume that they'd never get caught? Maybe they knew that they wouldn't get caught in europe. [1]
Then it's a good thing that we have prisons.
[1] when my wife lived in Germany, she drove some old beater that wouldn't pass the safety inspections. A friend told her how to pass: leave a bottle of Jim Beam on the back seat.