It pretty much says it in the title.
Some games for more than 2 players obviously cannot have a clear outcome if one player abandons the game. However, that does not need to be the case with 2 player games. While the result of a, say, chess game may in many cases be clear for some 40 years before the actual checkmate, it may be frustrating to the winning player to play the more or less unsurprising endgame phase only to see that the opponent abandons the game a few moves (or even one move) before being mated.
This is the case not only for chess, but any 2 player game. There is no reason to not make an abandoned game a clean victory for the other player, including a full ELO recalculation.
Some games for more than 2 players obviously cannot have a clear outcome if one player abandons the game. However, that does not need to be the case with 2 player games. While the result of a, say, chess game may in many cases be clear for some 40 years before the actual checkmate, it may be frustrating to the winning player to play the more or less unsurprising endgame phase only to see that the opponent abandons the game a few moves (or even one move) before being mated.
This is the case not only for chess, but any 2 player game. There is no reason to not make an abandoned game a clean victory for the other player, including a full ELO recalculation.