The genetic predisposition is not the sole cause of alcoholism, or it's not obviously what makes us wanting to drink in the first place. We start drinking for many different reasons, socially or because we have a problem. The genetic predisposition means that we get hooked to alcohol more easily, due to our increased tolerance and chemical imbalance in our brains. Once we get physically addicted, our body and brain change, adapting to alcohol, which is needed to function normally. This in turn makes it more difficult to stop. Curing the psychological distress doesn't make us stop drinking, because of the physiological addiction. This is why psychological therapy on its own inevitably fails.