You know your list of "good reasons" that companies should have for turning someone down? There is someone willing to argue with the employer that that's a dumb reason when they get told why it was why they weren't hired.

And the candidate often has this idea of "if I prove to the employer that their reason for not hiring me was dumb, then I win the argument, and then I get the job!"

Really, the best a candidate can hope for is to get the reason, and then walk away without talking about it. But because candidates want to make the company "defend their decisions" the employer won't even bother starting a conversation that will have no good outcome for the company.