because people judge gamblers to be stupid people, why they risk their money to gamble, which sometimes can make all the money lost, and people think why they do not use money for investment or other business. so for good, gambling will be called a negative thing.
Actually many people when get addicted to gambling they do not think for their family and they spend all of their money in gambling that is why when someone is involved in gambling then people think that they may addict so they think of it as negative.