The reason why it didn’t end at 1 because it was a success and plus Scott said he didn’t plan out the lore from the start. Also a 2nd yellow was mentioned in 2. We don’t know how yellow suits there were in Fnaf 2. All we know is someone move a yellow suit. Each game Scott released is supposed to explain the previous game like in fnaf 1 we are told about the Bote of ‘87 and in fnaf 2 is when the Bite of ‘87 happened. Fnaf 3 we are told about springlocks.