As I recall, one reason the Allies wanted unconditional surrender to be sure the defeated nations would accept that they had in fact been beaten and not "cheated" somehow out of victory. German resentment for the surrender in 1918 expressed itself in the conviction that the nation had been betrayed and could have won if the fighting had only continued. The idea was that an unconditional surrender drove home the point that one side had truly lost and would accept it.