They can simply bet high on low house edge games then recover their losses from the rakeback of their loyalty rewards. I’m sure a money launderer account will be a whale user with max tier VIP level.
I understand where you are heading to, but let us also not forget: There is no 100% sure game in gambling. Even if we bet on games with 1 odd, which reduces our chance of losing and increases our chance of winning, we still can't be 100% guaranteed that the game will come out positive, which is the reason why anyone thinking of to launder money will first of all think of other options, before they can think of using the casino.
Another form of financial activity, which requires users to deposit and withdraw, makes it much more easier to mix coins than casinos offer. Exchanges of coins, if not for the fact that they offer KYC, are the major means I know many use to launder and clean their money. So for the casinos, it can still be use for such, but the chances are highly minimal in my own opinion.
Casinos can't be used to launder money without being traced, since the funds would go directly to a wallet address. That's for crypto users. Then the receiver still has to mix the crypto to be anonymous. Main reason the government is working hard on following up those mixers, it's the end process. Due to the fact most gamblers still require Kyc to deposit funds in any casino, just like in exchanges, casinos isn't a safe place for money launderers. Even, not all casino restrict withdrawals for gamblers, some casinos allow users to deposit and withdraw without gambling or winning a bet. Money launderers prefer mixers due to lack of KYC. Once those details are collected or even when fake documents are submitted, they'll be trails or traces. Where the law enforcement agencies find it difficult to trace a criminal is when they've left no loopholes of any kind. I think Op is just curious about this due to the recent ban of mixers. Because this forum get tagged whenever a mixer is closed by the government. It's bringing a bad name on the forum. Promoting casinos isn't wrong, we see ads on stadiums, TVs, radios and bill boards regarding casinos and gambling. Remember, the government use the money to finance the health of addicted citizens and the nation.