A crypto hack can also happen to big exchanges, like it happended to Cryptopia, a big exchange from new zealand where huge amounts of crypto funds were stolen from people that had their coins stored on the exchange when the hack happend. All users that had withdrawn the fund before were safe because they stored their coins in their own wallets.
Even big exchanges are no guarantee that they can't be hacked, so better be safe and store your coins yourself.
Storing your coins safely will prevent your coins from getting hacked and you won't lose your crypto by exchange hacks.
It's the rule of the thumb, and it's been proven time and time again, we will see more hacking in the future and if your coin is in your wallet, you have a lot to be sorry, that means you are not listening to advice that exchange is not the best place to store your coins.