Well I guess the thrill, excitement, fun and etc. that they get whenever they play, Keeps them from doing it again and again. Also, to add the fact that they adapt to the idea that you could easily earn money in gambling.
Add to it the chance of winning is one of the very reason why gambling is addicting. There are people who mostly make themselves surreal in gambling and make it as their part of living. I wouldn't say that it is easy to earn in gambling but it is only by chance.
I almost ruined my life because of addiction but family was there to help me, and now I am happy gambling knowing my priorities and I know gambling is not my priority but just a way to have fun.
Those people that are making gambling part of their lives are the one that becomes addicted. It's hard to make gambling as your source of living when it comes money making.