ghost jobs are analogous to (the now illegal practice) of spoofing trades in equity markets, where they exist to manipulate the market to get an information edge about price and availability of the commodity (talent).
even though I think it's wrong, and in a consistent regs regime it would be illegal, like spoofing in other markets, it's the artifact of incentives created by outdated regs and conventions that didn't keep up with the scale of tech.