The majority of people that bought a wii i.e non gamers traditionally, had long lost interest in the original wii let alone buying a successor of some sort..
I know the common narrative is that the Wii brand was dead when Wii U launched, but going by my own experiences, I don't think this was the case. As late as 2012, the retirement home I was working at still had Wii bowling nights every week. I also still saw Wii games being played at parties all the time (primarily Brawl, NSMB Wii, MK Wii, and Just Dance). And whenever I stepped foot in a GameStop, parents were still coming in and buying Wii games, even after the Wii U launched (I remember overhearing a parent coming in asking for Mario Kart for the Wii, even after MK8 had come out)
I honestly think casuals were actually
too satisfied with the Wii, so much so that they saw no need to pay $300+ for a new box (if they actually managed to figure out that it was, in fact, a new box, and not an addon, lol). The Wii already did what they wanted, and better graphics are not a selling point to them. On top of that, it had a confusing new controller that effectively negated what was so special about the Wii to them (motion controls).