Maybe it's asked before, still, it will help us a lot.
Why do you gamble?
Why do you do not invest that money instead?
Why you do not donate them?
Because you are bored?
Because you are looking for entertainment?
Because you are going after the big score?
Why?
It varies among people of course but their main goal is probably to win. We humans want something that has a chance of giving us larger returns that is why gambling was still there. This psychological factor makes us to bet even more specially when we experience to win. That feeling satisfies us.