In football it's probably useful to jump up and down and be excited during a game, but in chess your emotions will make you play worse. So (in the case of professional players) they sit there for 5, 6, 7 hours and stay calm and focused. You can't just flip a switch and suddenly be excited as soon as the game is over.
There's also fatigue. After a long tense game OTB I mainly feel two things: relieved and tired... and usually more tired than relieved. Look at the face of a long distance runner when they cross the finish line, they probably look like they're in agony too, even if they just won. The celebration comes later after a good meal and some sleep.
And it's not like chess players don't smile after a game... it's just... they're not going to jump up and down.
A few months ago I started regularly watching live streams of chess tournaments and I noticed that after every game, the winner strangely seems depressed, whereas the loser's face expression can only be described as downright suicidal. I mean I understand that the winner can't jump up and down and scream like a football player, but at least they could smile? Or show some other semblance of a positive emotion? I just think this is extremely weird and wonder why chess players never seem to be happy. Can anyone explain? Thanks. :-)