Not many people actually listen to something called a Tutorial so they changed the name to Single Player.
HA ! Too true. It's rather baffling how many people skip the tutorial because they "just want to play the damned game." And then, lo, you see people asking in chat channels how to do things that were supposed to be informatively explained to them.
Am I still one of the few who actually keep and read their instruction manuals? Maybe my fondness for them is just the byproduct of many drives home from the game store when I was a kid. Nowadays companies seem to treat the manual as an afterthought -- 8 pages, with no color in sight.