There’s no way you can get your profit when you violate the casino ToS but you have the right to receive your original deposit.
I ask this out of ignorance. Is this always the case? Can't they claim damages to keep it?
Nope. Far as I know, most casino have it in writing [that the user agreed] on their ToS that if one or two clause were broken, they have the right to confiscate everything. Those who let the "violators" get their fund back were doing so as a good-will, not because they're obligated to do so.
For this specific case, if we assume that OP did violate the ToS, the casino has right to deny any fund that OP owned, it's there in one of their clause,
The suspension or deletion of User accounts shall not entitle Users to any claims for compensation, damages or reimbursement. In case of heavy misconduct, which include, but are not limited to, exploiting bugs, games or security holes, all account balances of terminated accounts are forfeited in favour of 500 Casino.
Now, moving to OP's topic, I assume no one invite UserU to this thread? Allow me to send my regards, then.