The longer and more involved I get in automotive diagnostics and programming as a hobby, the less I believe there is any particular conspiracy against independent shops and owners in the automotive industry (versus in the heavy equipment and ag industry, where there absolutely is a conspiracy).
The threat model most automotive systems are designed against (when they are designed against anything at all) is absolutely not "we want to screw over those damn independent shops trying to run diagnostic routines!" - it's "how do we lock down the immobilizer, the ADAS, and protect ourselves from tuning-related warranty fraud." Independent shops and individual enthusiasts are just caught in the crossfire between thieves, ADAS tampering, and manufacturers/insurance/regulators.
The threat model most automotive systems are designed against (when they are designed against anything at all) is absolutely not "we want to screw over those damn independent shops trying to run diagnostic routines!" - it's "how do we lock down the immobilizer, the ADAS, and protect ourselves from tuning-related warranty fraud." Independent shops and individual enthusiasts are just caught in the crossfire between thieves, ADAS tampering, and manufacturers/insurance/regulators.