There just is no yes or no answer to this question.
If the reason someone drinks is obvious,or there is a really good psychiatrist to get to the bottom of it. I think the why does matter if the reason can be found fairly easily.
But in my case it just really doen't matter,because the only reason I ever found was that I am an alcoholic. I tried to stop drinking many times over my 30 year drinking career. I quit 4 years ago,and I really don't know why I stayed stopped this time,while I failed sooo many times before. But in all honesty,I think deep down I really didn't want to quit.
So while I would like to know "why" I am afraid MY only explanation will always simply be that I'm an alcoholic.
Fred