Tesla has a history of aggressive behavior, so I don't think it's as clear cut as you make it out. Witness the guy who plugged into his ethernet port, found references to the Model 3, only to have Tesla remote in, downgrade his vehicle firmware to one that didn't have more references, so he couldn't discover more information, then disable his ethernet port completely, and send him a letter about his "unauthorized use of the car".

That wasn't protecting themselves from litigation. That's saying "this car is ours, you just get to use it, and we control how".

Just like you cannot get a service manual for Tesla vehicles. Except in MA, where it's required by law. Where you have to make an appointment, go into their office, and view the manual on-site, and can't take it with you. I believe you also have to pay a fee to do so, or at least did.

Of course it would be nice if Tesla could just release some sort of API for giving inputs to their cars, coupled with a cast-iron waiver that makes clear that they are not responsible for any consequences or damages.

However, they know that won't hold up in the court of public awareness/opinion, and that if people messing with their Teslas end up causing lots of problems, that legislatures and regulators are more likely to clamp down on self-driving cars generally. Which is the opposite of what they want.