Yes it is beneficial for them if people lose in their casinos, but that is really up to the gambler if he wants the casinos to profit from him. If he just wagers small amounts of money then he can have fun and not make the casinos super rich already. Just avoid it if you don't really have money to lose.
I totally agree, many gamblers made a gambling site or casino owner very rich. Being addicted to gambling is a really bad habit, but we can't do anything with it. From what you have said, maybe not just the owner, but the investors too. There are a lot of people investing to gambling sites because they now that it is a hit, and where most of bitcoin is being used.