I think that if a person adheres to the rules of his religion, then he will not play gambling. The rest can gamble either for fun or for making money. Because it is very difficult to combine earnings and entertainment.
It totally depends on the religion and their belief. There are other ways to entertain ourselves if we are just treating gambling for fun but because there's money to risk it became exciting. In my view, money that earned from gambling is not different in other source to earn, its just that how you accumulate it is more on luck since you have no assurance if you'll going to grow your money or not.
Many people do not care about the religion and only care about what they think is right.
If gambling is not allowed in anyone's religion, then the profit from it will also be wrong and illegal.
Many people think that you should work to get the money and anything which you get from speculation is not the right form of income.