I think this is common at bc.game because they often ban accounts when players get big wins. People who actively play in bc must know this. One of the best ways is open case in casinoguru and trustpilots, on this forum also
I don't think a big win is a reason to close a user account, the problem is when the users abuse the casino to win big, i have seen some users creating multiple accounts to abuse the bonus and after the win is when they get banned and start complaining. If a user break the rules the casino is in their right to block the account, and users must understand this rule, when a user deposit on the casino the money now belongs to the casino and not to the user.