They're forgetting markers for when the official canon adds something that completely breaks something you wanted to write and you either have to come up with a way to write around it or come up with some half ass way to incorporate it.

Or just throw up your hands in frustrated surrender, and say "this is now an alternate universe fic, where we'll all pretend that the new canon doesn't exist."

Gotta hate it when new canon elements break an essential plot point of the story you're writing.