To keep the story suspenseful for the readers up till the end.
Explanation:
The term "medias res" refers to the process or act of starting a story or narrative from a crucial point in the story, which is normally in the middle of the story. This means that medias res starts the story in the middle, in the midst of things.
By starting a story in the middle of events, the author maintains a sense of suspense in the readers. The readers do not know what is to happen, nor are they given any background story to let them understand how the story had been till that given point. This piques the interest of the readers, keeping them hooked to the story till the end.
