Gambling addiction can start with greed, chasing loses, being overconfident to continue gambling when you're winning. But it can develop if the gambler doesn't have self control, if a gambler don't know when to stop it becomes a very big problem. The gambler can keep on degenerating and keep getting worse, at that time they need external help to support them to get through it. People should be sensitive about the attitude of their loved ones, if they find out that one of their own is addicted to gambling they shouldn't condemn the person but show love and support and they can seek professional help if possible.
You are right and the causes you name are the most logical , sometimes it is a mixture of all, with respect to a person who has fallen into addiction, whoever it may be , Family, friends or strangers, they should never be judged, they should be helped , but they must be clear that they have to change, that they must have the desire to get better from that condition, it is something that we must see, if the person does not react or does not do their part, then they are already failing and other much more rigorous things must be applied.
In that situation, as long as the willingness to change and a self-will to help his own the needed help will be applicable and surely will weight in to the process of changing thier ways, addictions developed when a gambling submit himself into gambling without any limitation, when the desire and lust developed the dominance of addiction take place, the only way that it can be cure is when the person decided to change his way, with the help of his relatives / love ones the person will pass thru this, it's a process that needed time and understanding.