Because multiple drafts are not a thing.
One draft, multiple edits.
I know it sounds the same but it’s not. Once you have written your draft, even as a panster, you start analysing what you have, and apply your technical skills to improving that draft. This is part of the writing craft.
Planner: a writer who does the technical story analysis before the first draft.
Panster: a writer who does the technical story analysis after the first draft.
If your ending is screwed and you don’t know why, you have only two options:
Learn more about story arcs, story structures and character development.
Pay someone else to do it for you.
Just launching into another draft, hoping this time it will work, will achieve nothing. Except, maybe, another version of the story that needs fixing in a different way.