There might be people living off on gambling wins but they'd soon run out of luck and end bankrupt and might even go insane or turn into a criminal.
There is a huge distinction between gambling that provides job opportunities for people AND people who gamble as their main source of income.
In the former, like you mentioned, it provides job opportunities to millions of people around the world. Not only does it contribute to the people but provides revenue for the country as well. The latter, however, is entirely different and significantly risky. They live around the edge wherein their main source of income is based on 70% luck and 30% skill.