In recent times several users from this forum have complained about the account being banned on most of the casinos, so am prompt to ask what caused this situation sometimes the fault is from the casino site, and other times it is from the user itself.
It's exactly as you wrote, sometimes it's the user's fault, and sometimes it's on the casino's site.
Seriously, you should ask this question in a better way.
After all, an account is based on an agreement between user and casino and there is no third party involved, so there always must fault of one side or the other. Well, unless it would be a criminal case, then the reason may be authorities.