Almost every one of those vacant jobs has a offering price - a salary attached to it. so those jobs are only vacant at a price. That price may be unrealistically low.

There is almost no cost, in any negotiation, to making a lowball offer. So you have to question how many of those jobs actually exist. Just as low-ball offers in a distressed real estate market are unserious, a job that cannot be filled at an insufficient salary isn't really a job.