I think that one of the big reasons people will stay in jobs they don't like is that the prospect of applying to hundreds of positions to hear back from a handful of them and go on a few, select interviews is even worse than staying. Job hunting sucks.
And it's probably not much more fun for the folks doing the hiring, either. Trying to find the right person from a stacks of resumes and calling around to the various references has to be a nightmarish prospect. But it has to be done!