Don't tell them this in malice or anger, but do tell them.
The truth is if the problem is management then it's very unlikely any meaningful changes will ever be made.
I agree that it's unlikely. But if nobody says anything, then it's even less likely.
One truism of business is "The higher the management level, the less truth you hear." If you're on your way out (having another offer in hand that you're taking), your downside for telling them the truth is very small. Management might listen. It's unlikely, and even if they do it still won't help you any, but it's still worth the attempt.