While this is common I still think this is wrong, I mean look at online casinos, they do not give loans to their customers and yet they are a thriving industry and it would not surprise me if they were generating now more profits than land based casinos, so trying to take advantage of gamblers in this way by giving them loans may work for a time and increase the profits of that casino, but I am sure there are many gamblers out there that if they found out this information they will decide to stop gambling at that casino out of fear this could happen to them.
online casinos will never provide loan facilities to their customers because that will be very risky because so many customers come from countries that prohibit gambling, so even if they provide credit card guarantees or KYC it is very risky for online casinos.
it's different from land-based casinos, in that the country or city certainly allows the gambling business, so it's only natural that land-based casinos provide loans to their customers. and I'm not sure if gamblers would avoid the casino if offered a betting loan because we know that not all gamblers are sane minds but many gamblers will accept such an offer.