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.
I don't know if you have heard about Macau in Asia or 3 big casinos in the Philippines. So it's not just westerners' but big Asian whales as well are the main target now of the gambling industry.
That's why this sort of consortium of gambling company are willing to open to 3rd world countries to operate and the government are willing to cooperate because of the the tax or even to attract tourist.
Each time government seen good outcome for taxes they will cooperate with any types of business,even they've stake people's condition becoming addicted they will allow it making the industry becoming more and continues to grow from time to time.