You are right, no casino will purposely sell off their customers information to scammers because the casinos are already making too much profit from their company and I don't think their is any amount of money that scammers will offer the casino that will make them sell their customers information. Although, in some situation, it could also be possible that the staffs of the casino could be greedy to the extent that they will steal customers information from the cosino and sell it to scammers just to make extra bucks.
there is only a small chance that it could happen at an established and still operating casino. but for casinos that might go bankrupt or be indicated as a scam, it is very possible to happen.
I have several times received incoming emails from casino platforms that I don't know. and as far as I remember, I only used that email to register for the casino, not for other activities. they offer deposit and spin bonuses on certain games, which we usually see in casino promotions to new users.
I don't mean to accuse all casinos of doing this, but I often create new casino accounts just to try surfing. maybe one or two do.