Super Mario Maker producer Takashi Tezuka stated during E3 that they decided to add Super because the current game is (obviously) has more feature than the E3 2014 demo so people will know how different it is. However, the biggest reason is if they just call it Mario Maker, people will think they could create any Mario game level, like Mario Kart etc. So they add Super to explain the game is only about Super Mario level.
Full story http://www.technobuffalo.com/2015/06/29/nintendo-explains-why-they-added-super-to-the-mario-maker-name/
Sorry if this thread has been made before.
PS: Actually the information is coming from GameInformer, however the link didn't work so I use this instead.
A handheld gamer only (for now).