As I understand it (sorry, I don't have a citation handy) was that VW was gaming the tests, but in order to make their vehicles' operations MORE efficient. That is, the tests are dumb because they concentrate on start-up emissions with less attention to warm running. VW wanted to also optimize the warm running, but to do that they had to game the software to still appear to optimize only for the cold start.
That is, aside from the ethical problem of cheating the regulation (a big aside to be sure), they were acting more responsibly than most.
VW's cheating is in essence the cars have two modes to run the engine; compliance mode and performance mode, and they run in compliance mode when the car starts up until the steering wheel is turned (more or less).
In compliance mode, the engine control follows the rules to meet the emissions test standards. In performance mode, operating temperature is allowed to increase, which increases performance, increases fuel efficiency, idles better, etc, but increased operating temperature leads to more NOx emissions.
Additional, for models with diesel emissions fluid, performance mode injected much less DEF than compliance mode; DEF reduces operating temperature as well as directly reacting withe NOx. This reduced use of DEF allowed a smaller DEF tank to be used; regulations require passenger car DEF tanks to have enough capacity for normal use within the regular service interval; if the vehicle was operating in compliance mode the whole time, you'd need to fill the DEF tank between oil changes (or have a larger tank, which needs to fit somewhere).
In the end, the big tradeoff is fuel efficiency (and therefore CO2 emissions) vs NOx emissions; which is a fine tradeoff to consider, but you can't give drivers what they want and regulators what they want without cheating.
This is so irresponsible of you to just assert without evidence, and is so out of context to portray VW as the good guys here. They did not break the rules and flaunt regulations to make their system more efficient. They did so to cover up their failure to deliver on a new generation of "clean diesel" tech. VW thought they could do it, they invested billions in it, and they couldn't figure out how to do it without emitting way too many other pollutants. So they built their cars to lie to regulators.
The tests cover an extensive range of use cases, mostly warm running. There were two modes, one that was more fuel efficient but emitted NOx above regulations, and one that was less fuel efficient but was within NOx regulations. They detected when the tires were on suspension that simulates real-world driving for testing. They got caught by academics who wanted to test real-world vs simulated suspension.
Here is actual source, Bloomberg, which isn't some kind of environmentalist or anti-business publication: (https://web.archive.org/web/20160312181801/https://www.bloom...):
"The road tests captured a variety of conditions: high elevations up Mt. Baldy; stop-and-go urban errand-running in San Diego; freeway driving around Los Angeles. The two Volkswagens’ emissions exceeded standards by 5 to 35 times. The BMW’s didn’t. [...] The Lean NOx Trap is a system of concessions. To get cleaner exhaust, you’d need to use a squirt of fuel every few seconds to burn up nitrogen oxide. Or, in the other direction, to get better fuel efficiency, you’d need to spew out dirtier exhaust. Managing this trade-off requires a complex calibration of the onboard computer, the engine control unit, so it can adjust constantly to variables like temperature and speed and optimize both emissions and fuel usage. The trouble was, Volkswagen hadn’t been able to get its new engines to comply with the stringent U.S. standards."
The reason is they had invested in a "clean diesel" engine tech that was supposed to be their market differentiator. VW invested billions into it. Yes, it was more fuel efficient, but it was supposed to also stay within existing pollution emissions regulations. Nobody else made such big investments in clean diesel because they couldn't figure out how to make it more efficient without also emitting pollutants at much higher levels. But everybody was so bought into it that they felt they had to cover it up.
Before the shift there was an influx of tiny cars with tiny diesel engines which had emissions <= 99grams CO2 / km.
Now it's NOx all around. In fact, The Netherlands has limited daytime speeds on highways to 100km/h vs 120/130km/h just for this purpose.