So at this point I decided to bring it here to know or see different views from different intellects here on why do some people hide just to gamble or if it is the best way to gamble ?.
On another thought, that could be for their safety and the safety of the money. The huge sum of money in an open place is so risky. They might be trying to guard it carefully so that the bad heads will not get info of it to easily to rob them of their money. In that kind of setting, simple household tools could be used by evildoers to rob them easily. They are even there at the risk of their money and personal safety.
Lastly, rules are rules, and should not be changed for any reason. If you already know the rules in that setting, then obey them by bringing the exact money you want to wager to the floor. If not, you should be forced to wager the excess amount.