Motion Plus was too expensive at first

[Words Of Wisdom]

Sky Render said:
Actually, the Wii is Nintendo's biggest payoff since the NES. The SNES was not that big of a success; after the NES, in fact, it has a huge letdown financially speaking. It was still profitable, but only a shadow of the NES' profits were raked in from it.

The NES also had more diverse competition where it was easier to separate itself as unique from the rest of the market.  The SNES faced a pretty strong console opponent and even had to overcome Blast Processing.  The SNES did very well.