Mostly are due to the owners trying to be cheap or their driver hazraat actually pocketed the money for repair or if they are gray imports the dealer who sold them forgot to tell them that they are not tuned for this country.
Fill in = tesht lemp, shaart, frequency matching,chota sensor, nitto tape in general sentences and you get the perfect example of the cars you mention. For diesel MB - I have seen that most techs did not even know half the time what the scan tool was telling them. Worse with NAG1 gearbox, they would go about claiming to change the gearbox for simple repairs.