Welcome to Sober Recovery. I hope you can find some solace in these pages.
Why? I think they enter this vicious cycle. Drink and neglect really important things in their life. Like people. Then the guilt and shame is relentless, so how to deal with that? Turn to what they have found comfort and/or escape in. It only ends when they say "gotta do something different" and they not only mean it, but stick with it til they are on the other side, the beautiful side, the side where you hold yourself accountable, and you deal with the transgressions in the only way that there is: directly.
I hope you can find peace soon.