GAmbling is fun because its thrill unlike other boring game.. but not all gambling games are fun like dice game its boring to play in dice game..
It depends on the person doing the gambling. because everyone's tastes are different. for instance I am very pleased to do the lottery, dice, gambling and poker. but not necessarily you like what I like. So we give a motivation to them so as not to get carried away into a great defeat
Scientifically, what makes gambling fun is because of the adrenaline rush that we feel whenever we gamble and anticipate to see whether we win or we lose, more if we actually win. We're not actually addicted to the game (well, it actually plays a part) but we're getting unconciously addicted to the feeling of that adrenaline rush.
Well, that's just the scientific part of it. Personally, people get addicted to gambling because of the possible winnings that they can get.