You made all that up. Why?
Radios these days are software defined. They can sit on the same chip that uses a trusted bootloader and also provides an engine control module. Marketing departments can and will bend and pervert engineering specifications to highlight the consumer benefits and minimize the profit motive.
QED
Assuming you can even get to the antenna without special tools... you're just going to cut the antenna so short that the radio can't get a signal? On a hunch?
What if the SOC in your vehicle has to download a rolling encryption key every week in order to activate?
Going back and forth with measures and counter-measures besmirches the point. Cars have to be serviced and this may be considered just another aspect of it.
I'm not suggesting that this sort of thing is necessarily a good thing(tm) but, it may be viewed as such by some and it's possible.
Isn't it the consumer's prerogative and responsibility to decide?
Not to mention, lawsuits and PR nightmares can be factored into a business case analysis. VW actually went ahead and defrauded the US government in diesel-gate and they're still an almost $100 billion company.