Most of the countries actually putting bans on gambling are for religious reasons and that's why it's mostly the middle east region although it's not entirely pin on those areas but I think you get the picture. Other countries are actually utilizing the massive gambling industry which is something that the government are well known for as they always exploit situation to their benefits and one way they achieve this is by taxing the gambling industry which active initiative towards this.
I dont think religion is the main reason why most countries ban their citizens from gambling. Social effects is one of the main reason for gambling ban. The governments do think that high rates of gambling is a serious threats to the society. The consequences of addictions, financial stagnation and increase in criminal activities are cause through irresponsible gambling. It is the main reason why you see all gambling platforms emphasize on the importance of gambling responsibly.