I think gambling is addicting because of that feeling when you win big time! Not many things can measure with the thrill when you win at dice or even sports betting. I have increased my bankroll couple of times in my life by 400%-500% and these kind of winnings make you an addict.
It is really addicting because it is fun, you are making yourself happy while earning some money, but I'm not saying that you could always win money, what I'm saying is it is fun if you are making money on it, that is why it is addicting. It became more addicting if you lost a really big amount of money in gambling, so my advice to you is to know your limits if you are going to play gambling.