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 agree with you honestly. Most religious groups are on the motion that gambling is a sin, so I'll assume that in such countries, their government would as well be against it and since they have to power its much more easy to ban it completely. Honestly gambling is something any one can choose to do, so long they can bear the risk involved. The only thing I know that many gamblers fail is the fact that they take gambling as a means to make money and end up ruining their life's. Many governments who actually care about their citizens would go to any extent to cub what ever that would cause harm to them..