Accurate time-sensitive communication is very hard in my experience. I've heard thru the grapevine on a few interviews over the years, that often the interviewer gets the wrong impression on some subject. Due to the fact there are say ten+ candidates for a position, one wrong impression is often enough to torpedo your chances.

For example, I'm good at what I do, but not the kind of person to brag about it (hah). In fact I instinctively tend to downplay things I've done as no big deal. In some sense true, but in an interview it's enough to lose the offer. Trying to correct this but it is not easy.

Once I was referred to a position by a colleague, but didn't get it. Weeks later I heard, "not enough db experience." What? While I don't write SQL every day, I've used dbs consistently over decades, know the theories, etc. Sure, I might need to hit the manual for a week to get up to speed, but that is incredibly common and no hurdle whatsoever.

So, post-interview feedback is good, but asking questions/feedback during the interview itself would have been a lot better. I wonder if (when there are so many candidates), interviewers don't want to revisit past assumptions and prefer to just get on to "the next one."