V-r0cK on 25 June 2015
I've actually asked this question and somebody told me that Nintendo does include a large number of their own made levels in the game so in a sense that could be like the 'campaign'.
I understand that Nintendo did it this way rather than making another 'NSMB U' with this kit included, because it breaks the cycle of having "one NSMB per gen". Like smash, mario kart etc... So to me that's fine Nintendo did it this way.
