Greed is addictive and a lot of greedy people are unable to stop even though they manage to get plenty and so is gambling and the people that regularly gamble. It's so addicting because you're greedy to win or regain your lost money and in the process you lose control of yourself and get addicted.
Because those people already had a chance of winning on any gambling game that they play. And they keep on playing looking for the chance that it will give them satisfaction plus the profit. In the end, they are not aware that it is making them addictive.