Obviously the short answer is that I drank because I am an alcoholic, but that doesn't really tell the entire story for most of us. It may or may not be totally useless to understand what made us drink like fishes. For me though, knowing how booze tricked so many into being its' willing slave is worth knowing for a lot of reasons.
For some of us, this is a question worth examining, so thanks for asking.
I grew up around a family full of alcoholics and hated the drink, and was disgusted by drunken behavior, for the first 20 or so years of life. I watched it destroy the lives of people I loved. So for me, there was never any allure towards the social aspects of drinking, nor the need to find "liquid courage" during my impressionable years. It was the exact polar opposite for me. I hated the smell and taste, and I thought people who drank were completely unusable, useless idiots.
I drank - in the beginning - because it was just so prevalent in my industry that I just got tired of being the sober guy, the dude missing all the good parties. The booze culture wore me down I guess. Life as a musician just seemed infinitely more fun with a bottle of Jack Daniels. So on my first real drunken evening, I understood that it was this socially acceptable excuse to be an irresponsible a$$ for a few hours a day. That fact alone sold me. Add to that the fact that I liked the way it made me feel -or not feel- (as someone else stated) and I had to admit - at the time - booze was a great coping mechanism for most of lifes' more profound nonsense.
Later on, I noticed how life started getting more exciting in direct co-relation to the amount of booze I could put back. I would end up more popular, people thought I was funny/cool/brave, and often I was admired for the things I accomplished while being pi$$ed out of my skull.
And let's not forget that - socially anyway - there's so much positive reinforcement for the use of booze to cope. The deck is literally stacked against those of us with a propensity for alcoholism.
At some point in my life, it became a very useful crutch. I would booze out of boredom, booze to alleviate the feelings of a tragedy, booze to calm me down, booze to sleep, booze to beat down some knucklehead, booze to get laid ... anything really.
It was only when I started using the sauce as nothing more than a necessary medication for emotional and physical pain that I started slipping into the abyss. And, as with all of us I believe, at some point the inevitable occurred - a switch in my head was triggered, and there was never again a day when alcohol didn't completely rule/ruin my life.