I guess because there is no "lessons learnt" or "how to interview" thinking-- just grab someone from the canteen "Hey bud, you doing the interviewing today".

(and if you think I'm exaggerating-- thats how Steve Yegge described it when he was interviewing at Google, though it migth have changed since then)

Some speculation: They have very little feedback about how interviews went from the rejected candidate's perspective. They withhold feedback about the candidate so even if they did ask for feedback, it would be uninformed. Those that do get hired are the ones that went successfully through the broken interview process so they propagate it to their candidates as if it's the correct thing to do.

Spot on. My hunch is you're correct.

My radical proposal is to record interviews, for later playback and study.

Ages ago, I ran for office. Very similar hazing ritual.

The recorded endorsement interviews were generally terrific. Only one of the unrecorded interviews was constructive; I wish it had been recorded.

The majority of unrecorded interviews were shit shows. Which then seeded more drama. I quickly learned to make my own recordings. Kinda like having dash cams.

This is exactly my take, too. Once someone is rejected, the communication ends there for fear of litigation.

And the spiral continues.

Time crunch, pressure to deliver while interviewing a large number of candidates, lack of feedback provided from the candidate, lack of formal guidance or training in what to look for, quality control over the hiring assembly line, sometimes people have a bad day, and so much more.

The biggest reason is lack of internal quality control. You can't record the interview for later review. Experienced interviewers do not observe or "crash" interviews so feedback can be given to the interviewer.