The answer to that mate is that they are entertained when they gamble - basic. Because this is the reason why casinos are being built in the first place. Rich people are entertained when they gamble using money that they can easily get back in their business and the like. That is the reason why they gamble and don't care owning casinos.
But owning a casino is good decision instead of losing money there, I personally would like to run a casino if I were rich there than it will be nice to entertain himself with this way, but entertainment is only purpose behind gambling and that is main reason.
Rich gamble for fun and not for profit.