I'm actually going to talk about why exactly this game begins in a new fazbear's fright..
The newspaper of Nightmare Mode in FNaF3 could have been a cover-up.
The newspaper says "last night" when the guard didn't see fire that night.
The mode's name doesn't mean it's a nightmare, There's no ultra scary stuff.
Now that we know it's a coverup, What were they trying to coverup?
Springtrap. The Purple Guy inside him. They noticed Springtrap had a human inside him, Fazbear's Fright went out to find other suits. Who were these other suits? The suits in the backroom of FNaF1. If there is an extra Freddy Fazbear suit then there is an extra suit of every other animatronic.
They found these suits and modified them to look like nightmare things. This is why they are nightmare animatronics, They are made to look like nightmares.