One of the reasons I don't type it is that, say, I resign, then the game is over. The game is not going to appear in my opponent's list of current games and therefore it's unlikely they will click on the game. It's over. Why would they? So they wouldn't even see my gg.
Face to face, I would always congratulate my opponent, win or lose.
Before you resign, you can type gg is my point, rather than just resigning and disappearing. Just my take, obviously most don't agree because they resign and skedaddle.
g.g.
Maybe these people just don't like losing. They are ashamed to say gg. However, I always say gg no matter what unless they leave.
It depends on the context and time controls. Longer controls (like daily) entail a higher understanding/expectation for small chat or courtesy like "gg" (or whatever form of congratulations is used). I usually play blitz on chess.com though - blitz (and especially bullet) has people in greater rush and some are simply on the next game by the time you type the first "g" in "gg".
Whatever the time control though, I feel that a more specific/longer message is more meaningful. I do not congratulate after every game. If I do though, "gg" means that I enjoyed our game. "Good game" even more so than "gg" - if you get a somewhat rare "Good game" from me, there is surely at least one reason. The ultimate in courtesy/enjoyment from me would obviously be expressed via a friend request, message, trophy sent etc.
I realize that not everyone will rank how much the game meant to them via the post-game message, but it is one of the things that I do; perhaps it is to add significance to lifeless interactions on a computer screen, but it makes me feel like I am expressing my experiences more, even if others do not catch my gratitude in the same degree as intended.
It's quite easy to type gg after a win or loss. Bringing back some courtesy into the game would be refreshing, even if it is online. I try to type this in after every match, however most folks don't respond. (Many times they want a rematch though) Anyway just a thought, it doesn't hurt to be a little polite.