HR has a reason for that. Yes, possibly lawsuits, but also there is a small minority of absolutely crazy people. It's a very small amount of people, but high enough that if you do a decent amount interviews, you will run into these people. When you give these people a reason why you rejected them, they will hound and harass the company in order to "prove" the company is incorrect in their assessment. They're why we can't have nice things.