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?
It is? In what other countries are we talking about here where a company escalates to the labor authorities to prevent you from quitting? Usually this kind of thing is reserved to harass visa holders, not native workers.