We're all different. We drink for different reasons, we drink different quantities, of different types of alcohol, we react differently to the substance itself, we work out, or not, we eat well, or not.. etc. There are a myriad of reasons, to answer your question.
I myself drank more as a way of self medicating emotional issues from childhood, managed to control it, and had a successful career. You might call me fortunate. However, I always had problems with relationships so never had a fulfilling marriage or a family of my own.
At age 60 I'm still wandering, and just now discovering and working on all of these issues. Now, who's the fortunate one? You have your whole life ahead of you. Enjoy it!