Back then, some casinos didn’t require any confirmation for deposits. As long as the transaction appeared on the blockchain (even unconfirmed), the account would get credited instantly. sounds convenient, right? But that’s where some smart gamblers took advantage and pulled off double spends, sending the same transaction elsewhere before it confirmed, basically reversing the original deposit.
I believe the casinos back then allowed this to encourage the adoption of Bitcoin through gambling and they paid the price for this because I can't imagine how many caisnos went bankrupt because of this. I don't understand why people will be this heartless things but that's what scammers do but it's good it happened then as it helped caisnos to avoid further disasters in the future because I can't imagine if this was still possible in the recent times that cryptocurrency gambling has become so popular that there are now more transactions and money in the hands of the casino. So imagine them losing all those money now because of double spending, that'll be too bad for the caisnos and can cause lots of damage.