My main characters in failed/incomplete/unsatisfactory stories are surprisingly reactive, that is, driven by events around them rather than by their own impulses.

That's not uncommon. Villains act, heroes react.

I hereby dub this the First Law of Fanfiction: Every change which strengthens the protagonists requires a corresponding worsening of their challenges. Or in plainer language, You can't make Frodo a Jedi without giving Sauron the Death Star.

It's already called The Law of Bruce, but it's stated a little differently.