Because it's like a comment that teases the losing opponent in the game.
I don't know if it's because of the cultural difference with the West because I'm Asian, but in the Eastern Go game, it's a basic courtesy that neither the winner nor the loser of the game express joy or anger.
I don't know if you're saying "gg" because you had fun after the game or if you're saying it's a good game because you won, but I don't see it as a cool sportsmanship.
I don't know if it's because of the cultural difference with the West because I'm Asian, but in the Eastern Go game, it's a basic courtesy that neither the winner nor the loser of the game express joy or anger.
I don't know if you're saying "gg" because you had fun after the game or if you're saying it's a good game because you won, but I don't see it as a cool sportsmanship.