So here it is...
Yes, GMs resign. But in bullet chess, they only resign when their opponent has a lot of time left. I can see where resigning is applicable, but I often do not resign. This is because I do not care about the result, I care about the play. If the person has me cornered, with a queen and a few minor pieces, and I have nothing, I play on to see how the person checkmates me. I often find it disappointing if an opponent simply pushes a pawn to promote for an easy checkmate, because it shows that they do not have good endgame technique. And there have been situations where a completely lost position has turned into a stalemate.
However this is in endgame, where the beauty of technique can be appreciated. I can also see the reason for resigning, if your king is trapped at the side of the bord in the middlegame, and you obviously cannot defend it. The act of resigning depends on many things, and should not be generalised.
It can be more fun not to resign in some cases. Like when you both enjoy a game.