It is true that nowadays, there are several restrictions imposed by the casino due to AML/KYC laws, but in the beginning, that didn't exist (online-casinos).
There have certainly been cases where people have used casinos (and even exchanges) to hide/shuffle the origin of funds, 'cause when you deposit crypto on a platform, your link to the platform's address ends and when you go to withdraw, you withdraw funds from different origin (from other customers). Unless the platform keeps deposit/withdrawal logs of all user operations and provides them to authorities when requested.
This can be done even by people who have no intention of doing so. But that's the nature of cryptocurrencies, so like it or not, it's difficult for authorities to track the funds (even if the person isn't doing anything outside of their country's tax laws).
I just want to say the exact opposite, it's so easy to track things since they are recorded on blockchain which is public ledger where no one can alter anything. So we general people may not have the access to those logs but I am pretty sure every casino and exchange keeps it permanently for these kind of legal stuffs. I would not pick cryptos if zi want to launder the money cause with fiat it's easier, untraceable.
