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.
That feeling of winning big time is making us to be popular in the web or chatbox but that's not really the reason why gambling is so addicting. Gambling is simply addictive the way it used to be. We are winning and losing and upon experiencing to win that much it's making us more happier and feels comfortable that next time we gamble we'll win again. And that practice is repeated until it becomes addiction.