Superhero movies lean towards origin stories because they're the easiest stories to tell. One person has power, spend 45 minutes explaining where it comes from and their early life, another 30 minutes on their interaction with "normals," and then 30 minutes battling the bad guy and you're done.
It's the "battling the bad guy" part that's the hardest to do well. I like superhero comics, but their big failure is their need to not just have a superhero, but a supervillain. And then many supervillains. And then quickly they veer away from what is actually their most interesting story, which is...what if there are a couple of SUPERPEOPLE among us? Too soon there are thousands of superpeople and that's no longer our world.