It's only a sin if you do it in excess just like drinking or eating too much. If you don't let it affect your ability to support yourself or your family and don't get addicted to it, it shouldn't be a problem.
It is not a sin, it is just a problem but not a sin, eating to much of drinking to much is not a sin. It will just make your health bad.
What bad in gambling is that it makes not only your health bad but if you gamble away all the money you hurt those who near you, your relatives, your friends, those who love you. I don't know if gambling is a sin, but it is a bad thing if you don't know how to stop, for sure.
It is a sin, if we are going to ask the Holy Bible, the answer is yes, it is a
Sin, though people are saying that it is not, but it is just people's opinion, what we have to believe is the Holy Bible, and not the people's opinion, and what you have said was true, this Gambling doesn't bring us any good fortune or good things, but it is the opposite.
Because it won't bring any good to us if it is a Sin in the first place and it is prohibited by our Almighty God, we don't need to do it, because it will just lead us on the wrong path, but since most of us won't believe this because they are still convincing themselves that this is not a Sin, and they would win back what they have lost.