In most under-developed countries, where there are few employment opportunities, people tend to try gambling to change their faith. That's one reason why gambling is increasing all over the world.
I don't think gambling is popular in under developed county. When people have money they can try options but when they don't have much to live then their options are limited. I guess westerners are the targeted customers for gambling industry.
Most poor country also have much activities of gambling in their countries and this maybe the reason those countries were poor now.And we need to be clear that not all the people in the poor countries were poor we can see many billionaires from poor countries also.