If gambling was a scam activity, then no one would have continued playing gambling. The rule of thumb is that Gambling will make few people rich and many people poor in very less time. So people keep on playing gambling in order to become rich quickly and they are also ready to take the risk which come with gambling.
I think many people poor is wrong sentence here. Most people who play control themselves, they lose amount of money they can afford in exchange for emotions and chance of a bigger win. They not become poor at the end of the play, they just payed for some entertainment.