It's not only the data, but also the continued promotion of dealer service lock-ins.
There are many modern cars where (for example) the "service in XXX miles" indicator for oil changes can't be reset except by the access-restricted and very expensive factory service tool.
Many independent shops already have to buy reverse-engineered tools to allow them to service these cars and continue to stay in business. It's clear that automakers are very interested in abusing copyright laws to force a monopoly on after-sales service.
it should be made illegal to force the use of a particular after-sales service dealer - monopolies never help the consumer ever, and although some things have arisen as a natural monopoly, car after-sale servicing isn't and shouldn't be one of those.
You can buy an ODB2 reader for ~$20 on amazon. If you are working on any car newer than 1990, an ODB2 reader is a standard tool in your drawer.
The real problem is, to change the headlights on my car, you have to remove the front wheels and part of the wheel well. If anything these shenanigans help independent shops. If they built cars to last and be maintainable, there would be a lot fewer independent shops.
An OBD2 reader doesn't work for proprietary diagnosis, only regulated/standardized emissions related issues.
The example I supplied (Service Now mileage indicator, not Check Engine Light) was a very specific one with Porsche in mind. Most post-2004 Porsches have no procedure to reset that indicator without using an official PIWIS ($13000 + subscription, if you can even get one) or reversed Durametric ($250 + illegal if automakers claim their software can't be reversed).
Another example of anti-competitive dealer software is "coding." Replacing the headlight control module in a BMW, for example, requires it be "coded" to the car's control systems. Many DIYers and independent shops use straight-up pirated BMW diagnostic tools, because again, the "blessed" way to do so costs thousands of dollars.
There are many modern cars where (for example) the "service in XXX miles" indicator for oil changes can't be reset except by the access-restricted and very expensive factory service tool.
Many independent shops already have to buy reverse-engineered tools to allow them to service these cars and continue to stay in business. It's clear that automakers are very interested in abusing copyright laws to force a monopoly on after-sales service.