From what I'm seeing, the hackers used the weak password accounts to access a larger vulnerability once they were behind the curtain. The company I work for deals with sensitive proprietary data daily and we are keenly aware that individuals should never have an opportunity to access the information if any other user. Things like single-user quarantining of data blocks are a minimum for security. Users log in and live on their own private island floating in a void. On top of that use behavior tracking to detect access patterns that attempt to exit the void and revoke credentials. That is also not even remotely mentioning that you have a single point of access entering thousands of accounts. That on it's own should be throwing enough red flags to pull down the webserver for a few minutes to hours. There is a lot they could have done.