That's the point. Owners of casinos want to make profit and setting transaction limits for gamblers is not ideal for business. I believe the gamblers are all adults and are solely responsible for their actions. It is in the place of these gamblers to put a check on their gambling habits because the management of these casinos will not help, all they are interested in is profit, profit and more profit because that is the reason the casino is existing in the first place.
The casinos hoping if all the gamblers are adults since they state if they must be 18 years old during registration, but they don't have any way to make sure if all the gamblers are adults. KYC is one of the way, but they can ask their parents personal information.
Although it were their mistakes, but still not all gamblers are adults.