The urge to participate in risky activities is an intrinsic part of moving into adulthood. Take gambling from them, and the same adolescents will start doing drugs, alcohol, engage in random sex etc. Also, they are extremely sensitive in this age, so you can't fake it for them, you can't just feed them with "simulated gambling and other forms of gambling-like behaviors", like the article suggests, because that would be a pill they won't swallow. They need something real. They want to do something what adults really do, and not just average adults, but the most daring ones, from their point of view.
In short, eradicating a problem, gambling in this instance, you can cause more problems to emerge, which are more severe than the eradicated one. So, forbidding your child to gamble or to drink beer, think twice with what he/she can replace it.
In my opinion the main reason for this is online gambling because now there is no need to go to a physical casino and back to home late at night. Your elders will definitely ask you where are you coming from. On the other hand even a student can play online gambling from his bedroom and nobody will know about it. Online gambling provided them this facility and thats why the number is increasing day by day.