Car company’s have been doing it for decades. There are legitimate reasoning; theft relevant parts for instance; you don’t want to enable vehicle theft and the “security through obscurity” model did work for a long time. Unfortunately for the manufacturers, most factory security systems are being cracked by locksmiths and vehicle rebirthers.

Another reason is for warranty claims. The manufacturer builds the cars to be the right balance of price, reliability, efficiency and performance. If you modify your vehicles ECU software, the engine may not be as reliable or efficient. If an “unauthorised repairer” changed the programming of the ECU, it can compromise the efficiency and reliability of the vehicle.

There are been plenty of accusations of “planned obsolescence” because a vehicle has died just out of the warranty period, after someone has fucked with the vehicle tuning.

Finally, the other reason, especially for Volume Manufacturers is that their vehicles are sold as a Loss Leader so they can make up the shortfall through aftersales. Some vehicle importers make deals with governments to lower tariffs on new vehicles, but increase tariffs on genuine parts, like what the Japanese industry and the Australian Government made in the 1980s.

Whether you agree with this logic is irrelevant; this is the reasoning manufacturers use for restricting aftermarket parts and labour.

When a “free-market” Aftermarket Aftersales industry causes the Genuine Aftersales industry to fail, Manufacturers will try to make up any losses through other channels, like requesting government subsidies “for the good of the local industry” or selling telematics data (which just “happens” to have personal user data) to data brokers.