http://i.imgur.com/201ohkV.png This theory is 100% speculation, so it could be wrong by the time Five Nights at Freddy's 4: The Final Chapter is releasing.
The culprit!
I just came up with this theory, though it may be wrong, that the Animatronics we saw in the recently released trailer had been taken home by Purple Guy, who was the creator of Springtrap’s hybrid suit as well as himself. I am certain that he perhaps damaged the animatronics while he took them in his semi truck on his way home. That was perhaps why he had to put the plans on repairing the original animatronics' data banks on the same week Jeremy was taking on in Five Nights at Freddy's 2.
The next clue of why The Bite happened was because Purple Guy was careless left the Animatronics in his house, thought that they were completely shut down. It was his kid whom stayed up at nighttime, tried to dealing with the coming-to-life animatronics as we see in the trailer and ended up to be the victim of "The Bite of '87", which many people believed that it happened with Freddy, Foxy, or Mangle back in Five Nights at Freddy's 2, again.
The third clue of why it also happened - it was the "unnamed suspect" that ripped out Golden Freddy's endoskeleton out of his suit and donned it on Purple Guy during the Night 6 of Five Nights at Freddy’s 2, which proved that the police had tracking him down for not returning the animatronics to their original place after several nights of loudly noise of the animatronics that roamed the house, searching for the people that disgraced them.
The reason why I was able to connecting the evidence between Five Nights at Freddy's 2 to Five Nights at Freddy’s 4: The Final Chapter was because of the purple fan that was seen in trailer, the house, the kid and the animatronic’s appearances. Sure, Springtrap was not seen, again, and we seen the "Plushtrap" as he was showed on scottgames site and in the trailer - that is the possible = that "Plushtrap" is the prototype or at least the model of the true Springtrap OR mini Springtrap, like the ones with Nightmare Freddy. Added to that, it would be the reason why we see Purple Guy that gone enraged at the event of Afternight Minigames, destroyed those who treated kids with the cares.
But again, this all can be wrong by the time the actually game is releasing. The stuffs in this blog page is all purely speculation as of right now. Thanks for taking your time to reading this page and your positive responsive and feedbacks.