People gamble not just for entertainment because of the chance to win big money. It is entertaining because it gives you excitement even if you lose in the end.
I agree with you, gambling get people excited to earn some money at the end of the game, I think people like taking a risk due to gambling.
Actually playing games online also can make people excited, like some people compete on a tournament with a big prize.
But if I will be having a chance to choose from Gambling and Online Games with a great prize, I would rather choose Online games since I know that I will be competing in such game because I have a skill to it. Saying that, I can say that I have a higher chance of winning that certain big prize on Online game than on risking my money on Gambling.