because you can make a lot of money out of it
It's not just about winning a lot of money. It's more complicated. They lose money, they end up chasing their losses. When they get to recover their loss, they feel good. Also getting lucky and winning big makes them feel good. This "good feeling" is what that makes them addicted to gambling.
Indeed, that is why most of the people who have tried gambling have gone addicted on it, the losses that they are having everyday is the one keeping them on the gambling world, believing that they could make a lot of money on it, but the truth is they can't, because they are going to lose most of the time especially when the odds is not on their favor.
Gambling is a very risky game, that is why it is addicting, we are getting challenged by the house, which is the reason why we are getting hype out and gamble more of our money, trust me, the only people who are getting benefited on gambling is those who are lucky on this thing.