But the again - these agencies might be solving an entirely different problem.
In some ways they are. Notably Japan has no concept of constructive dismissal, and companies have a pretty broad right to assign work and even to assign someone to work at a faraway office. There may be some anti-harassment law on the books, but it's very hard to get anything recognised under it, and if someone is just constantly assigned bad work, or no work, they have very little recourse.
And even if you could win a lawsuit, Japan doesn't do punitive damages or damages for emotional distress. So you'd be able to claim, maybe, lost wages for your time out of work, and... that's probably it.
EDIT: Come to think of it I'm actually not 100% sure about the legality of this, but they sure try it!