Nintendo games used to have long legs but with the WII U that situation has changed ... SM3DW is a FLOP for the most part seeing as how it's the absolute lowest in terms of sales in the series. BTW it hasn't even sold 2 million yet so your wrong on that part.
A game with almost 40 % of attach rate is hardly a flop.
If you include digital sales, Super Mario 3D World easily surpassed the 2 million mark. So, you´re the wrong one here