It seems very simple to me. The network would be controlled by custodians including exchanges and banks. And under an attack the network would be over: the malicious stakers can basically pay themselves and suffer no cost to continue the attack. Conversely with PoW there is a sustained huge expense to continue to perform an attack, and the PoW can be changed by a fork. I would never consider this to be acceptable. Not that ASICs run by China aren't currently an abysmal situation either, but that is only a problem because bitcoin has no privacy