1) Not including Wii Motion Plus capabilities since the start made them scarcely supported when they arrived later, this prevented the SW growth towards games with more precise and realistic motion control.
But while some existing users and many decs started wanting something more, the vast majority of users was fine, and Wii was still growing strong.
2) Ninty had survived brilliantly that mistake, but for some unknown reasons, it left in Ninty execs brains the pang of dissatisfaction, until they suddenly decided they really HAD to kill Wii. Iwata himself, after announcing Wii U, but too long before its launch, started mentioning Wii with wording that implicitly, but clearly enough branded it as at that time almost a relic from the past, while at the same time, despite strong 3rd party support, Ninty started pulling the plug on 1st party. Wii sales, still strong, suddenly plummeted, and what's worse, too long before Wii U launched. Wii U beared the Wii brand, but by its launch that brand was already unrecoverably tarnished. By Ninty itself.