I may not know why everyone gambles, but if I had infinite money, I would still gamble because I like gambling. Gambling gives me joy, I currently gamble with a limited amount of my monthly income, which helps me grow my money as well as enjoy it. If I had infinite money, I would gamble more because then I would not regret losing my money.
Gambling is not just because we have unlimited money or not. We choose to do it for some reason. That is why we can't tell if someone who has a lot of money will gamble. She/he might have no reason to do that as well. In fact, even if we gamble today, that won't assure us that when it comes, we'll still be gambling. People can change unless we're stuck in the world of gambling. In fact, I can't even tell myself I will be a gambler forever. Especially when I never find gambling enjoyable anymore.