There must be some old HR book out there with an example rejection letter that many corporate HR departments used. It was calculated to let you down easy, to avoid making you mad and miserable.
Point being, it was always rare that you would get actionable feedback from an interview, because it was always risky. Now it is just rare to the point of non-existent.
- you didn't meet our (technical) expectations
- we cannot meet your expectations
- you're qualified but we cannot pay that much
- you're generally qualified, but we need a Foo Expert today
The common letter one gets is "we chose somebody else who is a better fit". Sure, but what exactly fit better?
I don't think this is too much to ask for. Even that kind of feedback is non-existent, and I'm off wondering whether it's one of those or some remark I made or something else.
The most honest feedback I got was in small shops which didn't put an HR department between me and the CTO/CEO.
If after an interview somebody asks for feedback, I'll generally give it to them. The details are fresh in our heads, I can carefully calibrate my answer to the person's mood, and we can discuss anything that is confusing or upsetting.
Once we've filled the positions, though, it's much harder to give feedback. I've got a number of people I'm turning down, so it'd be a lot of work. Details are fuzzier. And often the real reason is something unsatisfying, like, "this person was marginally better in a few key areas; that added up". (If we've done our pre-screening well, almost everybody we interview is hireable, so often the true advice is something depressingly anodyne, like, "keep trying" or "more experience would have helped".)
But really, if you want feedback, I'd find some way to set up mock interviews with people you trust. There's a lot of feedback I won't give because I don't think the person is ready to hear it. E.g., I once interviewed a person who was a bluffer. They failed the pair programming portion of the interview spectacularly, to the extent that I ended it early. When they asked for feedback, I told them that they should definitely work on their TDD skills. But the honest answer would have been, "Go get a therapist and start working on your personal issues, because you have a pervasive character problem."
That's an extreme case, but hopefully you can see the problem. As John Scalzi says [1], "There are a lot of people who, when they say, 'I’d love feedback,' actually mean 'I want a hug.'" Those people can be very unpleasant when you give them actual feedback.
[1] http://whatever.scalzi.com/2007/01/23/what-to-know-before-yo...