Are you sure? Here in my country which is known as the biggest Moslem country, in fact the number of gamblers is considered as huge.
I dont think how religious the country is, it will effect the number of gamblers because people own free will on what to do regardless what religion they are in.
Maybe your country doesn't have a high number of committed Muslims. In countries like Iran, Saudi Arabia, and other Islamic nations, gambling activities among citizens are low.
You can see how China has many population, expect more people not gamble in such country than countries that have fewer population. Another factor are religions that forbid gambling, government in such country go against gambling.
Gambling is illegal in Mainland China. That migh be the reason why we have low number of gamblers when you compare it with their population. But I guess gambling still happens in China underground or illegally.