It's not just about security here. Many more problems are faced by different traders. Many times there are various problems in the account, which can be solved without much hassle. Honestly, when the whole system gets hacked, the security of your account will not keep your funds safe. The binance has returned the customer's funds, which is a good thing. But it also proves that binance can be hacked at any time. What if the amount of hack is greater than binance's insurance fund? That is why it is best to withdraw funds after trading.
While I won't argue the fact that Binance is hack proof, I think it's safe to say that no exchange's security is 100% hack-proof. We also can't deny that some exchanges are more easier to hack compared to others. Keeping funds in centralized exchanges has always been frowned upon in the crypto community. Also, a lot can go wrong even if one just uses Binance for just trading and their own wallet for storage with private keys.