Only writers are allowed to tell the story's without photos?
No, but there is a distinction.
If a news reporter writes down a story and starts adding things that didn't happen, greatly exaggerate the events or puts a subjective slant on something, then it stops being news and becomes an editorial.(See Fox 'News')
The same with journalistic pictures. You're allowed to take pictures at such a angle or with a specific technique that highlights the facts. But if you start taking pictures that misrepresents the facts or start photoshopping in post production, then it's no longer journalism but becomes expressive, i.e. art.
People who think of the World Press Photo expect journalism, not art.