>The point is that you are already tracked via your phone (which is likely kit in airplane mode), so there’s not a massive gain to preventing car tracking.

That's like arguing "you're already plastering your face on social media, why are you hand wringing about corporations/governments building a facial recognition database?". The difference is that the former is consensual/optional, whereas the latter isn't. Moreover, just because most people aren't exercising their privacy rights, doesn't mean it's okay for those rights to be trampled on for everyone. Most people aren't activists or journalists who need free speech protections, but that doesn't mean we can trample on the first amendment. Saying you don't need privacy because you have nothing to hide is like saying you don't need freedom of speech because you have nothing to say.