Let's just say that one time a money launderer does that and gets away with it. Place a bet with a 99% winning chance and win that bet to wager his whole fund. And he does that in a way that the betting platform is unable to detect him. That could be a one-time job. Because the next time this suspicious activity will be detected. Thus, those money launderer will not be able to do it again.

Gambling platforms have many safety features and pattern-identifying algorithm that helps them prevent such actions. They may limit betting numbers on how many times you can bet and with what amount. Also if such activity is found with any accounts, they might revoke or restrict that account from withdrawing any funds. These measures prevent those platforms from using as a money loundering platform.