From HR's perspective, why spend time writing about why you didn't hire somebody? There is nothing positive that can come out of it, it takes time and effort,

From HR's perspective, why spend time writing about why you didn't hire somebody? There is nothing positive that can come out of it, it takes time and effort, and it's possible that it will create a whole prolonged dialogue about something that is done and done. However, there's no downside for you politely asking for a reason why. On one occasion when I thought the interview went great but wasn't hired, I sent a polite and well-phrased e-mail to the HR department. It stated that I understand they didn't feel I was suited for the job, and that I was perfectly OK with that, but if they could provide me with a reason why it would aide me a lot in my job search. I got an excellent response back citing reasons why they didn't think I was a good fit, and it was actually quite helpful. So, try asking in a respectful manner that shows you are not resentful and are truly seeking to better your future prospects, and see what happens.