Honestly, if your first reaction to someone doing this is to never hire them again, you’re going to surround yourself with people that will never tell you when you’re fucking up.
There's a difference between constructive and necessary feedback delivered discretely, and destructive unnecessary feedback deliverd in public. Do you think this public statement is going to be more effective than a serious considered conversation with senior management before he left? I don't think so. What purpose does making this public serve other than to try and raise his own profile?
Yes actually. If you believe that your management chain is ignoring you, in a public company you’re looking out for the shareholders by making a case for ineffective management.
I’m not saying that’s happening here. But you asked for what purpose does making this public serve.
He doesn't work there any more, he doesn't have an obligation to the share holders and publicly trashing management is as likely to lower the share price as to raise it.
Corporations aren't people and if you bad mouth the company, especially in a way that gets press attention, someone in HR will put a mark on your record. Either a no hire, or a "requires executive approval", neither is helpful in future job applications. That said I didn't realize this was apparently a VP position, and execs live in their own consequence free world.