You owe it to them
I’m writing this as a message to all interviewers. If you turn down a candidate, for whatever reason, they deserve to know why and how could they have done better. I’ve attached an email thread conversation between me and a candidate who I turned down a few days ago:
If you turning a candidate down for any of these reasons — behaviour, mode of conduct, unprofessionalism, lack of skill-set, not enough experience, fake work or something else, it’s your responsibility to call it out and let them know why. Extend a helping hand and communicate how can they improve.
15 minutes of your time can help someone build their career.