I think the reason it seems to work more than it actually does is because it's worst-case reaction is covert rather than overt. Someone who patronizes me or tells me sweet sounding bullshit will probably get me to hate them in silence rather than fire back immediately, since I couldn't easily prove their intent. It doesn't mean it's any better of a situation, and may result in delayed retaliation rather than just getting everything out in the open.
Actually that sounds like bad NVC. The point of NVC isn’t to obscure what you need from the other person. It’s to frame it in a way that’s objective about what you need and indicating what having what you need will allow you to do/be/feel/etc. The objective description is to remove your own emotionally loaded or offensive language.
I’m sure the HR departments of the world are misusing it though as means to an end and at the cost of employees.
An interesting side effect of making the tradeoffs clear to the listener is that their cost-benefit analysis may still fall on the side of the status quo. Especially in the case of a relatively impersonal relationship like HR-employee, it’s likely that the employee will be fine with large amounts of inconvenience for the HR department as long as the paychecks still come on time.
