What you're also missing is that US legal system can bankrupt you financially and mentally if you're poor enough. Musk is clearly in the wrong there, there is no even gray area.
Doxxing is typically done from public sources, only very unusually it's some kind of uncovered private information (e.g. by hacking). Most of doxxing is piercing together public information and spreading it among the masses.
For example where I live there is a general law about harassment and it's broad enough to cover this case, to have that Twitter account closed, and to have the person tried at criminal court and at the very least fined and put under supervision, if not imprisoned - if it happened inside this jurisdiction, of course.
It doesn't matter at all if it's from public sources or not. A lot of things are in the public now - because of careless data handling, due to leaks and hacks, and a lot of information is easily retrievable with social engineering. Making a special Twitter account that automatically announces every move that a person does with their vehicle is really way out of the norm.
Our society should not accept this, not even if the target is a rich person. How do you expect people are going to behave to poor people if this is how they're allowed to treat rich people?