There's nothing in the company's interest to give feedback. It takes working time to compile this feedback and give it to the candidate. The candidate isn't going to interview at the company again until probably a year or more - if ever. And the company has a reputation risk if the candidate decides to revel this feedback and allege bias or ineffective interviewing.
The upside as others have mentioned is that good feedback means you may get to hire that person later (maybe not even at the same company, people remember you if you give good feedback, because it is so uncommon)
I’ve seen this and done this as a hiring manager at multiple companies.
If you are honest, clear, and direct, and your interview (key point) does a good job quantifying the candidate’s performance, and their expectations are well set before the interview, there’s little risk of a reputation hit.
I’ve had folks push back or disagree, but it’s pretty rare and I’ve never been worried about someone dragging the company into a spat.
