Sorry but if I finish a game where my team never touches point and doesn’t get a single kill, that was not a “good game” lmao.
I’ve said gg after a loss if both teams put up a good fight, but if I totally destroy a team saying “gg” seems more snarky than good sportsmanship.
Personally I just see it as a polite handshake kind of end of the game acknowledgement. Like hey we all played, we all tried, it’s over now, good game. If you play little league/recreational sports as a kid they make you do this at the end of every game so I think for a lot of people it’s ingrained politeness. Maybe sometimes it’s snarky, but almost anything else you could say is way more snarky imo. Bg, complaining about team, EZ, __ diff etc. are all the actual snarky ways to end your interaction with the other players.