Wii MotionPlus would have been too expensive to include at the Wii's launch.
In an interview conducted by VentureBeat, Reggie Fils-Aime, President of Nintendo of America, briefly talked about Wii MotionPlus. Fils-Aime revealed that when Nintendo was designing the Wii they already knew about InVenSense's gyroscopic technology that powers the Wii MotionPlus. Including the technology when the Wii was first released would have significantly increased the overall price. Fils-Aime explained that the cost "would have been unacceptable," and that the technology has only recently become affordable making Wii MotionPlus "a viable product."