Those who gamble also are forbidden in their culture. So even if the people gamble but they have this guilt feeling at the back of their mind. That they might loose their hard earned money.
Most religions have, along with the theology and the principles of the corresponding god or gods, some short of moral code that comes attached as a way of keeping the peace in the community of followers, and, to be honest, to favour those that dictate the rules. In that code, it is usual to mention the basics: not killing, not stealing, ... Some religions take that a notch further and pretty much ban anything that is fun. I am not sure the gods want us to be bored.
I am not sure about God wanting us to be bored but I do believe that God wanted His creation to be happy, prosperous, and free from all kinds of harm and diseases. Though one thing I can't find in the holy scripture is the exact word "don't gamble". Yes God warns us about being greedy but if we play gambling games with entertainment in our mind, are we being greedy? It has been long written in the history of mankind that many religious groups oppose gambling activity but yet the gambling industry continues to prosper. If we take the context of being greedy, even farming, fishing, or anything that produces money can be a sin so why single out gambling activity?