Because "higher level people" are the ones who make the decisions to do things like this, and they nearly always get away with it. The engineers who added the system are responsible, too, but at the end of the day, if they had said no VW would have found someone else to do it.

When companies act against the interest of the societies in which they exist, it's at the direction of executives, managers, or other "higher level people." If they're caught, their punishments sometimes don't even negate their wrongdoing, let alone match up to crimes which are generally less harmful to the rest of the world. They get away with it, and when they don't, it's not that bad for them. The lack of justice is infuriating.