Because if someone starts to be a bother after a couple of beers at the same time there could be someone even more drunk but remains quiet as continues to gamble more money. It would be interesting to know what the official protocol for these situations are.
Casinos have terms and policies which don't allow them to let a too drunken or intoxicated gambler play at their casino.
They have employees/staff to see and figure out intoxicated gambler by seeing like walking, speech, control and coordination, etc.
I found this site about this information but I don't know that all casinos have these rules or not.
https://www.business.qld.gov.au/industries/hospitality-tourism-sport/liquor-gaming/liquor/training/rsa/refresher/unduly-intoxicated/penalties