You're assuming that HN cares about ghost jobs. They don't. They make money by growing startups and selling them, not by respecting job seekers. So, why would

You're assuming that HN cares about ghost jobs. They don't. They make money by growing startups and selling them, not by respecting job seekers. So, why would they put any difficulty in the startups' growth? What's there for them to gain? In the end, it is "caveat emptor". It's the responsibility of job seekers to evaluate if the posts are trustworthy.