Definitely not always. It used to be that a mechanic or a skilled owner could tune, modify, repair or replace absolutely anything in your car. That was basically since the invention of the car, up to somewhere in the 2000s. And even then, various hackers and pirates made sure almost anyone could get their hands on the software. In fact, many mechanics these days use 3rd party software because the manufacturer refuses to sell them their version or even that version doesn't have all the features.

That is the recent (and gradually worsening) situation but it is not in and of itself a justification. Effectively you're saying "it's currently this way therefore it's okay for it to be this way".

Manufacturers have increasingly restricted control over products as they've gradually been digitized. Prior to the digital era anyone could do anything to personal property (regulations notwithstanding ofc); more expensive items typically came with circuit diagrams for the purpose of repairing them.