I think that, besides the Pathetically Drunk hero in all of these movies, the common factor is the woman who loves him. The heroine who finds and falls under the spell of whatever humanity remains in our wastrel hero. Sure, we are hoping he gets it together, and sometimes he does, sometimes he doesn't, but the heroine always manages to find her way. She manages to stand up and say, "Hey, I love you, but I have to take care of myself and I am not going to let you fuck me up along with you." Okay, it's been so long since I've seen Leaving Las Vegas that I'm not sure that happens with Elisabeth Shue, but it does in the other three.
Here's the thing. In real life, there is nothing sexy about loving a man who could choke on his own vomit at anytime; and who can't be counted on for anything. Fortunately, my own beloved doesn't fall into this category of protagonist. But there sure are plenty of drunken men (and women!) and plenty of women (and men!) who try to make it work. Call it optimism, call it insanity, whatever it is, some of us must have some sort of an "If-He-Love-Me-He'd-Change" mutation in the genome. I've been to an Alanon meeting...I know this is true.
Well, anyway, it makes for good cinema. Happily Ever After? Not so much.