I knew, I had received a welcome bonus but didn't know about the requirements until I was about to make the withdrawal, a pop message warmed me that I was going to lose the bonus if I decided to proceed with the withdrawal. I didn't mind. I lost it but withdrew my winnings
You’re lucky that you only lose the bonus amount because some casino usually deducts all the profit made during the time when bonus is active.
So can only withdraw your bankroll in the end. New casino usually have this feature and I lose a lot that was supposed to be profit because of this BS rules on casino bonuses that is not clearly indicated on bonus ToS.
I think why their allow him to withdraw his original money from the casino and deducting the bonuses is because he have not start using the bonuse he got to gamble and all his winnings comes from his main deposit without any bonus, had it been that he used a percentage of the welcome to gamble at all, the casino will never allow him to make the withdrawal unless he meets the requirements for withdrawing winnings from bonuses, to avoid all of those bonuses requirements that is the reason most gamblera always avoid claiming bonuses like in this guy case.