The first theory is they actually have a good team of professionals to secure the exchange system. But the technology keep fast moving forward so do the hacker so they try to find the vulnerabilities on the system, in fact, white hacker and bounty hunter get paid to find a bug.
We can't call the security team a good team when their task to secure the platform failed. If they are a good team no matter how fast moving the technology is, they are able to cope up with it and at least is one step farther than hackers.
It is very possible that the hack can be an inside job. One of the security staff maybe plan the hack and leak out the vulnerabilities of the platform security so that hackers can easily bypass the security and exploit the platform fund.
Exit scam through hacking incident is also possible since users will have a hard time finding out that the project owner themselves hack their own platform.