I personally found that trying to find the answer to this very question was one of the things holding me back from getting sober. I desperately wanted to know "WHY" i was an alcoholic, and I spent agonizing hours researching it on the internet, reading books. etc. In the end though what I really wanted was to fix the reason "why" and start drinking normally again.
For me the only answer that allows me to live my current life is "because I am an alcoholic". Why other people are not alcoholics is irrelevant because I am.
Ask yourself this James - what would change in your life if you did know why?