Whoever keeps millions on a centralized exchange is an idiot, period.
All big traders are holding coins on centralized exchanges, and if you didn't notice Coinbase exchange is custodian for most Bitcoin ETF's so far

It has been proven time and again that keeping significant amounts of money on centralized exchanges is not safe, no matter how reputable that exchange is. Trading has always been the most speculative topic in this regards cause decentralized platforms don't offer the liquidity required and traders wisely cannot keep withdrawing and then depositing back when they want to trade.
So, I can understand why one would want to keep funds there, but would still advice against it.