For me, my "why" was that I had reached a state of physical dependance. I literally had to drink every day in order to keep my body from going into severe withdrawals. Heart palpitations, dangerously high BP and heart rate, etc. I got no pleasure at all from alcohol anymore as i was basically in a maintenance mode of keeping my BAC up to a sufficient level to stave off wd's but stay conscious. There was no "buzz" or relaxation involved anymore.
The bottom line though is that only you can decide when enough is enough. It's pretty much a guarantee that the consequences will get progressively worse if you keep drinking. But also consider that you already know things are better if you don't drink, right? Addiction doesn't follow logic though - which is why you hear so much about "acceptance". And not just from twelve step program followers. No matter what method you choose to quit drinking, even if you don't have a formal "method" - you need to accept the fact that drinking simply is not an option in any quantity. Something is different about us - maybe mental, maybe physical, maybe genetic - maybe something we have no idea about - but we simply cannot drink alcohol in a safe manner anymore. You don't even have to call it acceptance, but you have to come to grips with that fact on some level. And accept that it can never be changed.