Excuses are common when people leave a job or a significant other. Rarely does a disgruntled employee or boyfriend give his real reason for leaving. (Unless they have a fiery temper and just want to get revenge by spouting off.)
We all tend to avoid painful or confrontational moments, and it’s all too easy to fabricate some silly reason which everyone knows is illegitimate, to avoid having to address the real issues.
It takes unselfish, objective consideration to gently share what went wrong when you’re already on your way out the door. You won’t benefit from the new policies or the changed attitude, but you are giving your aggravator the opportunity to understand what went wrong and then to (hopefully) not repeat that mistake.