A person can deserve an explanation even when the decision itself will not change.

People are owed reasons even when reasons will not alter the outcome. An explanation is not only a step towards changing a decision; it is a recognition that the other person is affected and capable of understanding, and withholding it treats them as an obstacle to be managed rather than a party to what happened. Refusing to explain is its own message.

If you have to deliver a decision that is genuinely settled, say so plainly and then explain anyway. Say this is not going to change, and here is how it was reached. It is harder than a vague non-answer, and it leaves the person their dignity, which is often all that remains available to give.