For an exchange, people deposit their money into the exchange, you just hold it, and the more they trade the more of their deposit they give to you as profit, from the trading fee. That means even if there was a hacking, it can't be that big, how would people withdraw it from your accounts, and even if they do, at some point you will stop them or move the money out. So, it doesn't make sense on HOW they lost this much money, they must have done something stupid for sure.
It is so simple. SBF embezzled the FTX users funds. He used it to support politicians, loan his firm Alameda Research and hide suspicious transfers to fund many investment of his own company. The hacking incident is very suspicious probably it is one way to hide that FTX funds is already sucked dry. Aside from that, another surprising is that the FTX has no Bitcoin holdings. I wonder where are those BTC that FTX users have bought and keep in their exchange.