if you were an experienced/mature tech employee you should probably know that there are real HR reasons why companies are strongly advised not to give too much information in a rejection email. there is only ever downside. your reaction here is a potential red flag.

i'm sympathetic to you, it sucks, why cant we all be nice to each other, and my answer to that all is lawyers.

It could also be that they might be sued for stating the real reason so they went with something that would be dismissed if it went to court.

> … specifics around the interview and where the candidate did not perform well …

Takes time away from the day job and other candidates.