I did not own a Wii, but did buy and actually really enjoy the Wii U. Many games I really like playing to this day (Splatoon, NSMBU, 3D World, Pikmin 3, Breath of the wild, Rayman Legends, Mario Maker, Lego City undercover, Mario Kart 8, and more I am missing). I even find the gamepad fairly comfortable to use myself, and use the pro controller still on my switch.
I think there are multiple reasons it didn't do well, but would have liked to see it do better since me and my family have gotten a lot of entertainment from this system.