^ As I remember correctly because I don't have enough knowledge on technical stuff on BTC transactions. The 3 confirmations consider as safe and can not be reversed but this is only for small transactions like $1k below. However, in large transactions like millions of dollars in BTC amount will need six confirmation, this is the standard for most transactions to be considered secure. It would be love to use a gambling site that offer for free withdrawal fee and I hope all of them are generous enough to have that free fees upon withdrawal.
I would like to know how many gamblers in the crypto operate with amounts of millions of dollars. In my opinion, there are very few of them and they are unlikely to be anonymous, since if the casino makes transactions of several million dollars without knowing the information about the client, it can be accused of money laundering.
That's part of it, gambling sites will automatically ask for your KYC if you have such amount of transactions, if the site do have the permits the regulations required this information.
Not sure what are the set up but like what you have said, it can be accused as money laundering if that huge amount just passed by without any knowledge about the owner of that money.
The site also needs to protect their business for sure complying with the law is far important to them.