They've undoubtedly pleased an English teacher or two along the way, and they've found some satisfaction in telling stories or at least in writing scenes, in putting words together to convey some visual notion or emotional experience. If they didn't, it certainly wouldn't occur to them even to want to write. But being able to write a scene isn't the same as being able to write a whole book. I could imagine scenes with the best of them. But I never really had to worry about it going anywhere.
Books have beginnings and endings.
That means they have middles during which things happen. Middles are terrifying to beginning writers. Imagine, for example, what you would feel like if you were writing a story about two people meeting and being attracted to each other and having a conflict and talking it out and resolving it in five pages or ten. You've got a story, perhaps, but you don't have a novel. And I used to worry what would happen if my people actually got together and talked.