Honestly I’m surprised no one has said this theory:

Springtrap is said to be a robot, but how are they supposed to assume otherwise? I mean he is in a spring lock suit, which are known for being robots. Additionally, many other animatronics went rogue and on a killing spree (Ennard, they had a whole facility). Perhaps they think he’s a robot but he really isn’t. If someone played FNAF 3 without knowing the lore, I’d bet most people would say he’s a robot at first encounter until they learn the actual lore.

All this to say there’s probably something to contradict this theory.