However I would say that IMO it's another case of foreigners buzzing by depicting boring and common stuff under a "weird Japan" light.
Shitty companies manipulating employees to stop them from resigning is something that exists in any country. And this escalating to the labor authorities or going through a lawyer is not a rare thing anywhere either.
It happens more frequently in Japan because the culture of not being confrontational is strong. The fact that lawyers can afford to specialize in this matter alone is just a logical result of the larger number of customers.
EDIT: I also want to add this: if you have been in a company for a while, you are eventually going to see or hear about how resignation is handled for other employees. If you want to quit and already know that the company is going to harrass you and make your life hell, is it so weird to save your time and mental health to delegate all of that to a dedicated professional?
I have never heard of it in the US. I’m sure some examples exist but I’d be really unpleasantly surprised if it’s a major social issue here.
Pretty universally illegal. California doesn't have noncompete clauses at all. Texas, the state I'm most familiar with, doesn't allow them to be enforced except for skills that are proprietary to an employer, .e.g., supporting specific software in a specific way or something. Pretty sure most states that have them are the same. Making burgers isn't going to do it, and nobody would sue you over it anyway, they'd sue the new employer whose lawyers will know better.
I have had an employer try to get me to sign an illegal noncompete before, but that was because it was a small employer who didn't know the law. When I quit I politely informed him that it was unenforceable. He didn't try. That doesn't mean employers who know better don't try to intimidate employees, but they could just as easily threaten to break your kneecaps. Probably they won't.