Giving people feedback is not always a good idea. Sometimes the information just helps them to hide something from the next person they encounter.

This is true in many domains, I think. You should not explain to the conman how you saw through his lies. That will help him fix that and con more people.

You shouldn't tell people in your dating profile what turns you off. They'll just avoid revealing they have a third arm if that's one of your turn offs.

I think interviewers have incentive to help people they like but no incentive to help someone they don't think they want to see in the candidate pool down the road.

Maybe they will point you to things you can learn if it will make you a better candidate but not if will just help you tune your pitch.