The reality is that most gamblers, and specially the most addicted ones, are usually people without much money to begin with.
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 have to agree on your point. While gambling also entertain us, but majority still gamble to make money, and you won’t expect for millionaires still aim to make more money as they have it already. So what they are looking for is purely to have fun and relieve theirselves from stress, and once they get over it, they will not gamble more often, hence they are not prone to addiction.
But for low income earners, they gamble to make money. But the more they gamble, the bigger the losses they’ve been acquired. Eventually, if they lose their self-control and discipline, then gambling addiction will follow.
If we compare then yes I would agree with the idea that more people put the goal of earning in gambling than the idea of just having fun, one of the reasons is because there are still quite a lot of other things that can be made into entertainment without involving the possibility of losing if for example what you want is nothing more than to seek pleasure, but what happens? yes the population of gamblers is increasing and I am sure that there are some of them who hide behind the idea of "entertainment" where they actually come to "multiply". For the rich I'm sure that most of them just use gambling as a place to fill their empty boring time because logically they already have a sure way to actually make money such as from the various businesses they do that eventually make them rich, so this is quite reasonable to be the reason that the rich mostly use gambling as a place to relieve stress for a moment.
Background can be a triggering factor about the purpose of someone coming to gambling, such as those who have low finances in their lives which I think it is quite reasonable for them to assume and assume that gambling can be used to make money, or even some of them instantly believe and say that gambling can be used as a medium to change fate, but the fact is that gambling is not for that, which in the end yes instead of earning but what happens is that they experience a lot of losses.