It's quite unusual that even at this day and age, with a lot of techniques and new practice on safeguarding a platform, hackers are still able to get through even with the robust of security systems. I wonder how tight their security are and what their system admins do for the hackers to still find a vulnerability on the platform. Also, this stresses the age-old question of whether to keep your funds in an exchange or not, and the answer is laid right before our eyes every time a theft occurs.
there is nothing unusual about it because simply there is no computer security system in the whole world that is impenetrable. every system has some weakness. some have less and some have more but all of them can be broken into and when the incentive is high enough (in this case a large amount of money) there will be lots of attempts.
besides, most cases of exchange hacks were fake news where the exchange itself tricked their users and stole their money because they were going bankrupt and wanted to save their asses.