It took exchanges time on the order of weeks to cease trading. During this time, Andy was able to apply massive hashing power to the old chain to catch up to the new chain and surpass it - and since the exchanges were still running the old wallet, he could then dump as many funds as he liked into exchange wallets, where there was nothing anyone could do to prevent him from dumping them. And dump them he did.
So what about the people who bought those dumped coins, which are deleted in the fork? They are in the exchanges now, unless they get reimbursed, the users won't see the coins that they paid for.
Is there a plan to repay the exchanges?