For one, a literal story teller can use all the body language, vocal tones and facial expressions they want to convey what their characters mean, which you must find another way to do in print. One way is to include some illustrations, which is very common in children's books, but that is not "writing". (It is authorship, but not writing.)
Secondly, a verbal story tends to be a very short story, without much plot. Most children's books are a few pages of text, at most. Some for the very young are barely a half a written page, a poem.
It takes about 200 pages to make a novel, and many published "short stories" are still dozens of pages.
Those are just more difficult to craft and to pace.
Thirdly, verbal stories tend to "teach a lesson" or describe an adventure for characters that do not really change at all. Winnie the Pooh is not really transformed by any of his stories, does not become an adult, or wiser, or broken. It is just "adventures". But by the end of "Huckleberry Finn", Huck IS a different person, and has overcome the racism he was taught to believe in by his childhood culture, through his exposure to Jim.
In the novel form, things change, and readers expect characters to move from state A to state B through conflicts.