Possibly because in ancient times incest was thought of differently than it is today. In ancient times, towns or villages were smaller and the world as we know it did not exist for them...for some the people they saw in their village or town were the only people they knew existed. In order to procreate and keep their civilizations going, incest was practiced to ensure good bloodlines - or so they thought at the time.
I'm not sure but I guess thats because they were uncivilised. In a civilised world nobody would practice incest anyway..
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.