The government couldn't completely ban gambling because government itself also supported gambling to some degree. For example they have given license to traditional casinos.
Even when they limit the teens to gamble online there are still holes to this laws since they are not able to watch out every online development which gives an opportunity to o businesses that allows anyone to register.
The license aren't gotten for free, thousands of dollars are put on the line before any casino can be legally operational in any country unless they want to be doing illegal and by that, they can be sue in the future and not just that, casino pay tax to government quarterly and yearly, so government are the big benefactor of gambling in the society in my opinion.
Gambling has helped some people whether we want to admit it or not, there are people that has a change of life because of gambling but we also have people whose life has ruin because of gambling and it's a choice not force, so we can't completely say gambling is bad to the society. If you wish to play it, it's your choice and decision.