Gambling is not sin but it comes in category of norms just like telling a lie is considered bad habit and a liar is not welcomed in any society same gambling is a bad thing. It is prohibited in many societies by religion perspective just to save people from being victim of it which creates problems in society. It is kind a moral valued thing more than sin, in simple words.
For me gambling is a sin, because why are you gambling? Only for fun or profit? We are going to be honest we it the main reason why people are gambling is that they want to have a lot of money because they are hoping for it. And we all know that the love of money is the root of all evil things. So, when you run out of funds for your gambling needs then you can do bad things just for it.
Maybe some for fun and charity, in my country(I live in Europe), casino revenues contribute to taxes, for helping the poor, refugees, and unemployed people.
Many old people play slots after they got the change, playing for fun, only a few can win, they don't care losing money because they believe their money lost can contribute to the poor, which is a virtue.