The answer is simple: they are not passionate about her. They've never been. Storm is constantly brought up in the movies because she is so iconic and
so beloved. They
know the fans want to see her. That's why they bait us with cool power display scenes in the trailers (only to give her 3 lines in the movie). I'm sick of this.
Rogue is another example of that. They actually released another version of DoFP and named "The Rogue Cut". They know how beloved and popular those characters are, they will be constantly bringing them to bait the fans, but the true is: they don't know what to do with them. Because they're only passionate about the three characters we already know.
Also, I don't like how they feel the need to change the characters to "make them more interesting". The idea of making a more "rebellious" version Scott shows they don't like who he is, so they need to change him.
That's why I have zero hope for Storm for now on. For Scott and Jean, yeah, I do believe they'll get decent screentime and development. Especially Jean. I'm not worried about them. But Apocalypse was the reintroduction of tthose three
huge characters and Storm wasn't introduced to be one of the main characters. She wasn't introduced the same way Scott and Jean were. They have different plans for Ororo. She'll be standing in the background with little to none character development. If her role indeed grows, it'll only grow to a supporting character like what Beast is now. She'll never be a leading characters, sadly.
I have more hopes for Kurt than I have for her.