If a company doesn't hire you, then by definition they have determined that your time is of no value to them, so it would literally be a waste of their resources to interact with you further.
It probably does affect them, though, whether they're aware of it or not. Some of the best talent they can get probably reads HN threads like these. A prospective great employee could easily read this thread, see stories of company X ghosting people, and decide to avoid them.
Not necessarily. Companies should be assuming false negatives in their process and should be encouraging reapplication in most cases. It is in their best interests to provide feedback to the developer and a good experience.
This may be internally consistent, but what of applicants following up on their applications? A sizable portion of the workflow believes - and is advised by job search coaches - that the correct response to being ghosted is to follow up on the application. Do you not waste more time fielding and diverting followup calls than simply sending (at minimum) a quick form email to remove all doubt?