because......
any choice in every bodies life is actually a gambling
choose a wise husband from a bunch of boys is a gambling
choose a school to study is a gambling
choose a boss to work with is a gambling
so, gambling is addictive
no one can escape...
I don't think anything other than the win feel and greediness on money. Once you have experienced winning some money from gambling and have seen too many playing with a huge amount and winning a huge amount multiplying the investment into 5 times, you will not feel like stepping back.