I think it's a valid question. So far, the three DLC packs to include a Map, Killer, and Survivor are all referred to as "Chapters".

Nurse, Nea Karlsson, and Crotus Prenn Asylum: The Last Breath Chapter.
Michael Myers, Laurie Strode, and Haddonfield: The Halloween Chapter.
The Hag, Ace Visconti, and the backwater swamp: Of Flesh and Mud Chapter.

Why is this?

If I were to take a guess, I think that, once all the planned "Chapters" have been released, then the "story" will unfold. Now, as to what the story is, I can't guess, but I would assume it has something to do with the primary antagonist and most significant yet unknown character in the game: the Entity.

Maybe the story reveals how the Entity came to be. Maybe it explains what it truly is. Maybe it tells the story of Survivors learning how to defeat the Entity once and for all and escape its nightmarish domain.

But hey, that's just a theory. A Game Theory!