half-baked theory i just pulled out of my ass: atem obviously ascended the throne pretty young and even before that, being a prince is a full time, stressful gig that requires a lot of composure and entails making a lot of hard choices/dispensing justice. he probably didn’t get the chance to just be a carefree kid and play games (non-life threatening ones, anyway) the way he no doubt would have liked to.
and that’s why (or part of why) yugi, his future incarnation, is the way he is: a pretty youthful, innocent kid with a love of games and a soft heart. strong without cruelty. the person atem would have loved to have had the chance to be