Business
When a rule is enforced through a predictable test, a company can make its product behave well only while it is being tested. Software that detects the test conditions can pass inspection while the product breaks the rules in everyday use. That is how such a fraud can spread across millions of units before anyone notices.
When leaders demand goals that cannot be met honestly and tolerate no failure, the people under them turn to illegal shortcuts rather than admit defeat. The pressure travels down the hierarchy until the people doing the actual work feel they have no option but to fake the result. In this case, engineers who could not build engines that met the rules installed software to fool the tests instead.
Once a company has cheated, selling the cheat as a virtue makes the deception worse and the eventual reckoning harsher. Here a company spent heavily promoting 'clean' engines that were in fact dirty. That turned a hidden technical violation into a public lie aimed at the very customers who cared most about the environment.