What VW did was to save money from ThinkBlue systems. Not every manufacturer failed the tests, especially the ones who used exhaust gas treatment did pass, and were more economical than petrol engines. After that, the EU changed emission standards and made them more strict, so VW switched to using dual exhaust treatment. Which made the cars more expensive.

What finally killed diesels was the removal of the tax reduction on diesel fuel. Since it is now taxed the same as petrol, there is no more any advantage that can offset the higher purchasing costs of the cars.

Same way that banking apps don’t care if you could screw up your account anyway, they will ban rooted phones just to avoid the risk. Because when something happens, what do you think is more likely? That the customer accepts full responsibility for using a rooted device and says that’s on me? Or that they blame the bank for losing all their savings?