Why does Nick retrun west after Gatsby's death?

Nick returns west after Gatsby's death because he is disillusioned about the people that surround him ("After Gatsby's death the East was haunted for me like that, distorted my eyes' power beyond correction"). He sees that Tom and Daisy destroy the people who become attached to them, and that Jordan Baker is no better. Nick questions whether or not people who grow up in the west are able to adapt to the east even if they try with all there might. He comes to the conclusion that they cannot, not in the case of Gatsby, Daisy, Tom, or even himself.