Video games can be fun but without having money on the line the excitement just isn't there. Most people gamble because of the adrenaline rush that comes with winning large amounts of money. But I guess you could combine both worlds and bet others on video games or bet on professional e-sport matches.
Well, most video games also provide quite an adrenaline rush, particularly if you are playing competitively.
I don't think the adrenaline rush is the major factor in this, I think the truth is most gamblers have the false belief in the background that they are going to get a lucky streak eventually and win big, truth is it rarely happens.