Couldn't you replace the exchanges in question with major PoW miners? The exchanges in question hold customer money, and customers could trivially move their crypto to their own wallet, or another exchange.
You can't even begin to compare a "major miner" with an exchange that holds a lot of users' funds. A miner has spent a lot of money and put a lot of effort to acquire that large hashrate while the exchange has done virtually nothing. Not to mention that the miner has a lot at stake while the exchange doesn't.
Don't you choose a pool to stake?
No.