Well, not everyone attracted to this game has played FNAF, such as me and the one you anwser to. Sure yes, most parts of the gameplay are not so difficult to pick up as you said. However, there're some spots in gameplay that confuse new players, especially the combination to fix light fuse. Even, I have reached level 8, I still haven't know that the combination is on the wall in the office untill I see your reply here.
I would sugguest, to have a simple guide book at least if many believe making tutorial is unnecessary for developing the game, because it shares similar mechanism with FNAF.