A story solves one of the least glamorous problems in language learning: repetition is necessary, but repetition is boring when nothing changes.
Stories allow language to repeat while the situation keeps moving.
Meaning creates memory hooks
When a word appears because a character wants something, discovers something or causes a problem, it is attached to an event rather than an isolated definition. Later appearances reactivate both the language and the situation around it.
Stories make prediction possible
Continuity narrows what might happen next. Familiar characters, locations and goals provide context that helps a learner infer new language without needing every word translated.
Controlled stories can engineer useful repetition
Beginner material has a difficult job: remain understandable while repeatedly using the vocabulary the learner most needs. A continuous story world gives those repetitions a reason to exist.
The same word can return in new scenes and combinations rather than appearing ten times in an artificial drill.
Eventually the training wheels come off
Graded stories are not the final objective. Their job is to create enough vocabulary, reading speed and confidence that increasingly authentic books become enjoyable.
At that point the learner gains access to perhaps the greatest repetition engine ever created: reading because you genuinely want to know what happens next.
Good stories turn repetition from a chore into momentum.