Well in short...because he is aware of how greatly his lifestyle has changed and also that he has not given as much attention to his roots as he should have. After all, if one doesn't remember his roots, he will lose his very identity. His empathy towards his sister's death is basically just nostalgia and a feeling sorry for her, more than any real affection towards her...they were never really fond of each other.
But what he felt towards Joe was always genuine. Even though he was quite embarrased of being associated with Joe publicly in his new society he could never forget how kind Joe had always been to him and the life that they had once shared together. So even though the promise that he made to Joe to visit him more often turned out to be an empty one, he meant it when he said it because he truly did love Joe and the relationship that they shared.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.