Kaiba: "Can't these people see this is just a card game?"

Yeah, you say that right before flying off in your BLUE EYES WHITE DRAGON JET! I'm not sure you're the best person to lecture our heroes on taking the game too seriously, Kaiba-boy.

Kaiba is unique among characters in that he has no outside reason to like the game. He's not mystically connected to it or able to discern card spirits or anything. He just REALLY REALLY LIKES CARD GAMES.