I would not consider it as a disease but just some form of psychological defect as the case may be. What happens is that gambling has a way of trying to gain control and once it is able to go through with that and take over your emotions and you let it do that easily, it would be hard to get out from.
It is not just gambling, as this is applicable to other things such as sex, drugs, alcohol, name them. It triggers somethings in you to just always want it more and if you realize that and still let it gain the best of you, then it becomes a problem.
What gambling does is that it promises you the jackpot as long as you keep on playing. It makes us think that eventually we're going to be millionaires, we just have to keep doing what we're doing and so far we're doing. It's the same reason why there are people who never forget to put a bet in the lottery. They're thinking, "What if today is the day?" and so they push themselves to bet even at the point that they have become aware that they are never going to win.
Sex, drugs, alcohol, and gambling, they all have one thing in common. They give you dopamine rush whenever you do them. Our mind wants to experience that dopamine rush again and again. One day we're good but after a couple of days our brain misses it. And the thing is, our brain slowly needs more and more dosage of it. It needs to have it more often. At some point, your brain becomes reliant on that just so that you're going to feel normal. This is why going cold turkey when you're addicted to something is really the hard way to do. Your brain is going to have withdrawals. It's missing the "drug" whatever form it may come (e.g. sex, drug, gambling).
Addicts didn't know that they are going to be addicts. They kind of just do their vices. They kind of just let it take control. They weren't aware that they are needing it more and more. So in their point-of-point view, it "
kind of just happened".