Neither party owes the other anything, but giving some sort of feedback, besides being polite, is a simple and useful positive contribution the other part's lif

Neither party owes the other anything, but giving some sort of feedback, besides being polite, is a simple and useful positive contribution the other part's life, namely because the candidate has invested time on the process. Much for the same reason, competent HR professionals appreciate if you give them a reason for leaving a recruitment process or a job, it helps them identify areas of improvement.