Raw processing power has been named as the reason why Nintendo decided against releasing NES Remix or NES Remix 2.
One of the easiest ways to answer that is to say, 'I was working on 3D World, which was developed on Wii U,” series director Koichi Hayashida told IGN when asked why the games only appeared on Wii U.
So I was already familiar with the system's architecture and developing for that platform lent itself to the early stages of the project
But, if you step into the shadows a bit more, in order to accomplish what we wanted with NES Remix, and get the effect we wanted out of it and the value that we wanted it to have, we needed some more machine power.
I think the Wii U offered that up for us pretty easily, and it just would have been more difficult to do it for the 3DS. I think that's really the answer. It's just that the Wii U had the machine power we were looking for in order for us to build the software we envisioned from the get go.”
NES Remix 2 arrives on Wii U's Virtual Console this week.