Having to give that kind of feedback just sounds horribly draining to me. I know there are people who would accept it. There are people it would really help.

Some would already know it and just say ‘thanks’.

But the people who argue with you that you’re wrong, or they need another try, or ‘I forgot to mention X’, or ‘you just hate me because Y’... the people who feel hopeless and you’re just ‘confirming’ their fears (even if they applied for something way outside their qualifications) or falling apart over it.

I would never want having to deal with that be a big part of my job.

I've rejected dozens of people right after face to face coding session of a simple task (third meeting, first technical) explaining the reasons, providing them some guidance on what to tackle next, if I saw hope invite them to try again once they feel they filled the gaps or at least describe the progress and ask if we think it's enough to try and/or what could be next.

I've most likely never had a person who left without a handshake with a sincere smile on his/her face and most of them expressed their gratitude.

Sometimes you have to reject a person on what you feel is a gut feeling. It's because over time you developed an intuition which is picking small details in a less conscious manner. In the end there are some reasons your intuition is shaped that way not the other and you can find something that presented within the context of your company and expectations will resonate with the candidate and he won't feel like he's been scammed.