Most millionaires would rarely gamble. As you mention, there's little point for them to do that.
They can instead enjoy many other activities with the money they have.
Gambling is basically paying for chasing the fantasy of becoming a millionaire, which they already are.
I also agree with that majority of people or rather gamblers who easily become an addict are those who doesn't have money and when they gamble they are ready to put in everything they have just to have a good wining but the rich doesn't gamble much and even if they do, they gamble with strategy of targeting a club that has higher chance of wining with a smaller odds and put in money but when it comes to the poor they gamble too aggressively.