The developers want players to experience the levels by playing them.
http://www.nintendoworldreport.com/news/40543/super-mario-maker-will-not-have-youtube-support
Nintendo has confirmed that YouTube uploading of level creations and replays will not be present in the shipping Super Mario Maker.
Super Mario Maker producer Takashi Tezuka confirmed the move in an interview with Game Informer. When asked why the feature would not be present, Tezuka said "We thought about having YouTube uploading, but it’s not in our game. The reason for that is other than just watching movies of courses, we’d rather players play them and experience them in that way."
Super Smash Bros for Wii U had uploading of replays announced for an upcoming update on Sunday.
Well, if "watching the game" isn't very fun, THEN I GUESS USING THE NINTENDO WORLD CHAMPIONSHIPS TO PIMP MARIO MAKER WAS FUCKING POINTLESS, WASN'T IT? ::) This sounds alarmingly similar to their bullshit excuse why they weren't going to have a story mode in Smash Bros. U ("Because everyone just went to Youtube to watch the cutscenes."). Nintendo, people are going to be recording & uploading Mario Maker Stages to online video services whether you like it or not. You can either get with the internet for once and let other people entice new players by showing off their latest creations, or you can waste countless time & money chasing people off Youtube with Copyright claims.