There's a funny thing about superhero movies: Structurally speaking, they're fundamentally different from superhero comics, just by the very nature of how they're presented to the public. Or at least, they used to be. Until fairly recently, the appeal of comics had always been in the continuity, the ongoing sagas that built on each other and were designed to run indefinitely as a long-form narrative. The movies -- even when they were designed to kickstart a run of sequels -- were always meant to be self-contained stories.
That's flipped around the other way over the past ten years or so, with comics often looking to provide low-continuity, self-contained stories to readers picking up paperbacks and hardcovers even as the movies build billion-dollar franchises by creating a shared universe that stretches across multiple forms of media. It's no surprise, then, that if you really want to see where that trend got its start, you can trace it back to Batman '89 and the influence that came to the comics when screenwriter Sam Hamm was tapped to craft a story for Detective Comics #600 and provided the blueprint for the modern Batman event in the process.