A chess game is over in at most about 60 moves. Sure the game might last for several hundred moves, but by move 60 only a few pieces are left and it is obvious [to experts] what is going to happen. Even in unlimited time controls, the actual time spent one all moves (as opposed to sleeping or doing some non-game activity while waiting for your opponent to move) isn't very long.

By contrast code lives for many decades. While it isn't all modified every day, it is changed often enough.