It is the main reason why we should not use a exchange as a wallet. People think that it is safe to just put their cryptocurrencies in exchanges but they do not think the risks that they can face. This is proof that even reputable exchanges can be hacked so be careful on choosing an exchange because of the risks and the possibilities of losing our money.
We need to use more cold wallets. I think a lot of people store crypto on exchange because they are not aware of infos like this or they just want to be in line with orders.