Don't be so sure. When Sony and Microsoft were both talking about their next-gen hardware (PS3/360) Nintendo made a very public statement that they had no intention of joining them and would instead extend the lid of the GameCube with innovative new accessories for game experiences you simply couldn't have on competing systems regardless of how powerful they were (similar to Nintendo DS versus PSP). This was in the era of Guitar Hero and Dance Dance Revolution.
Sure enough, you suddenly started seeing stuff like Mario Party 5 with the mic, DDR Mario Mix, Donkey Kong Jungle Beat with Bongos, Odama with the controller-mounted voice control, Donkey Kong's, etc.
It seems clear to me that the Wii Remote was originally intended to be an IR splinter for Chibi Robo, but they realized that it was far too innovative to be relegated to a subset of a failed system's small library. With some extra features (wireless, accessory port, accelerometers, etc) it could be the standard controller for a whole new platform based on the GameCube.
An accessory originally intended to extend the life of the GC ended up getting the GC rebooted as the Wii instead and it enjoyed far more success than anyone could have predicted. Looks like they made the right call.