Why did Steinbeck give more importance to the Cain and Abel than to the story of Adam and Eve in East of Eden

I think that Steinbeck is more fascinate with Cain and
Abel because of its implications on evil and the nature of being in the world. 
Certainly, the narrative of Adam and Eve is a part of this.  Yet, for Steinbeck, the
interesting element is how the children inherit the world given to them.  Cain and Abel
being the offspring of Adam and Eve represent how they interpret good and evil in the
world.  To this extent, Steinbeck is interested in how the nature of youth interprets
what has been given to them.  The development of evil, the lack of regard for another,
and what it means to be discarded are all implications that are reflective of the
descendants and inheritors of the world rather than with those who originated it.  For
this reason, Steinbeck ends up giving more importance to the idea of Cain and Abel and
where the role of evil stood with both of them than with their parents, Adam and Eve. 
As Steinbeck seeks to understand and transform the world from what it is to what it
should be, it becomes evident that the narrative of the children is critical in
accomplishing this end.