Excellent question.
Part of the problem with drinking alcohol is that the more you start to drink, you can start to realise you are getting into a spiral of decline.
You start to wake up in the mornings needing a drink in order to not feel ghastly and actually function at all. This starts to become a regular occurrence. You feel deeply ashamed that you can no longer control your drinking: it's controlling you. Because you feel ashamed, you then drink more so you no longer feel ashamed.
Welcome to the death spiral of alcohol addiction.
The only way of getting off that spiral is by admitting that you are an alcoholic. Not just to yourself but to your friends and family who may not even be aware that you are struggling.
You need to make it known to them because of the simple fact that you go to some family get together or other social occasion and it usually means alcohol is present (in the UK at least) and it's awkward when you're expected to be drinking and joining in with the festivities. If the folks around you know that you have an alcohol problem, then they wont try and encourage you to drink. If they don't know, then they can think you're some sort of killjoy etc.
Also, I declare myself an alcoholic on a forum like this as a form of public service. Anybody who suffers with an alcohol addiction is pretty much an expert on the matter. Even more so those few of us who are able to talk about it and possibly help others. You also find that you end up helping yourself by talking to others with similar experiences as it can occasionally cast a light on your own problems. It's essentially group therapy in action.
Most alcoholics can't do that, because they're pissed and many simply for the fact that they are lying in an early grave.