why?

why don't athletes smile when they are being interviewed at the end of a game? i am talking about the winning athlete? i have been watching basketball, baseball, football, any sport (you do know who i am married to, right?) and after the game when the commentator interviews the winning teams star player, they act so tough and don't smile while they're talking. i mean if i had just won a nail biter i would be beaming!!! beaming!!! anyone agree? just thinking about that.