Some dads can't think quickly on their feet. It is easier for them just to say 'no' than to explain why. They expect kids to accept 'because I said so' as enough of an answer. That's not fair to kids like you, of course. It might help to have a quiet chat with him again a while later, asking him to discuss reasons so you can understand.
He might think the game is too violent or will distract you from your studies or will tempt you to stay up too late at night or will lure you into online gaming ... all good reasons. It is a shame he's not explaining what he's thinking. Try and make it easier for him to express himself.