I experienced that many times when working in casinos, gamblers explicitly asking for more drinks, and even getting violent if you refuse.
When they are drunk, they can use violence to force the bartender to give them more drinks. They said that they need more drinks to make them focus on getting the win. But that is what happens in the physical casino, but we will not get that experience on online gambling because we never meet with the drunk gamblers.
Those waiters are also observing if the gambler is either consistently betting or slowly getting tipsy.
thats the reason why they are controlling the delivery of drinks.
Not unless the gambler will go to the bar in which they need to pay per drinks then that would be another case.
as they have the rights to ask as much as they want because they will pay for it.
That is the waiter's way to control the gamblers who drink because they don't want to see the gamblers will get drunk in the end. Besides that, if they can control it, the gamblers will not make a mess in the gambling place.
But still, the waiters will not allow the gamblers to drink too much, even if they have much money and can pay the drink. It is not easy to handle the drunker, and that is why they always need to control the drink.