Pay transparency law supporters have argued successfully that there is a compelling interest in closing gender and racial wage gaps and that salary range information can be mandated in job listings for that purpose. What's the compelling interest in this case that allows the government to control speech?
You could also argue there is loss to other companies listing real postings, as those fake ones add noise and people might miss their posting and not apply, causing them delays in filling their position.
Plus, if the ghost jobs are to appear to be growing to investors, or to satisfy regulators to justify internal positions or foreign hiring, now there is harm to investors or false compliance to regulations.
And I'd also say, the misrepresentation of demand, might lead people to pursue education in some careers and upskill thinking there is a lot of jobs for those skills, that would be a pretty hefty financial loss if they were mislead.
If move cross country because the job market in an area looks really good, only there aren't actually any jobs, what is the cost to me in the end?