There are so many examples the exchanges failed and customers lost big, I never store any crypto on exchange, only trade there.
And despite this people still insist to store their coins there, on the surface this may seem like a contradictory behaviour but what happens is that many people never really think about the consequences of their actions and they do not believe that they will get hacked and will lose their coins, so they keep their coins at the exchange believing their coins are safer there when in fact the opposite is the truth.
Any hacker knows that exchanges are holding a fortune and as such they are always trying to find a flaw in their security they can exploit, while in the case of a user as long as he is not a whale and he takes the time to secure his coins then the chances he gets hacked are minimal.