theirs which it would really be that normal that they would really be that confident on doing so but if its yours then its impossible that you would confidently selling out those information for mere amounts.
We do know on whats the result of leaked information or being compromised which it could really be used on other means or ways which it might really be putting you up in trouble.
There are lots of members in this forum who performed KYC just to have a sit on airdrops. So probably those people are not on their normal minds. Though I think those who doesn't think too much of privacy as a very important matter will give their information. You can find plenty of them on social media, even publishing their normal everyday lives together with their selfies and family, friends and relatives' photos.
This is also the reason why many got scammed especially with their other accounts, giving someone your personal information is not good at all even if you get paid for that, in gambling that might work but I still not suggest this. Though requiring some documents might be the last option for the site to verify your account there’s also a chance that the information you get can also be used by other gamblers since that person is selling his identity and that could compromise your account as well.
As long as the Casino is licensed and follows regulations, it cannot ignore the demand of the authority. they have to give-in in order to have a smooth operation. Putting myself in the owner's shoes, I would rather lose some players than lose my business completely. And besides licensed Casino are bound by the rule of user's privacy and they will have problems if they leak or sell their users' informations. It can also cause their licensed as casino operator so I believe reputable casinos will safeguard their users information.