Mario Kart DD was a pack-in game; so its sales don't count.
But anyway, Xbox as a platform has limited appeal and it reached that limit this gen due to Sony screwing up; no one outside of the UK or US will want its successor console unless it is for some pricing screw up on the Sony side again. Although I think Wii U is going to trounce Sony and Microsoft more thoroughly next generation than it did this generation if only due to the head start release which they didn't have this generation.
I describe myself as a little dose of toxic masculinity.