It had one of the highest attach rates of any Nintendo console at the time, only bested by the GC. Honestly, the whole "no one bought games on the Wii" is just something that's been repeated so often that people take it as fact
Based on the SNES selling 49.1m, N64 selling 32.9m, GCN selling 21.7m, and Wii selling 101.6m, we have the following attach rates of a few major franchises:
Super Mario: Super Mario World (20.6m, 42.0%), Super Mario 64 (11.9m, 36.2%), Super Mario Sunshine (6.3m, 29.0%), Super Mario Galaxy (12.8m, 12.6%), New Super Mario Bros Wii (30.3m, 29.8%)
Mario Kart: Super Mario Kart (8.8m, 17.9%), Mario Kart 64 (9.9m, 30.1%), Mario Kart Double Dash (7.0m, 32.3%), Mario Kart Wii (37.4m, 36.8%)
Zelda: Link to the Past (4.6m, 9.4%), Ocarina of Time (7.6m, 23.1%), Wind Waker (4.4m, 20.3%), Twilight Princess (7.5m, 7.4%)
Donkey Kong: Donkey Kong Country (9.3m, 18.9%), Donkey Kong 64 (5.3m, 16.1%), Donkey Konga (1.2m, 5.5%), Donkey Kong Country Returns (6.5m, 6.4%)
Metroid: Super Metroid (1.4m, 2.6%), Metroid Prime (2.8m, 12.9%), Metroid Prime 3: Corruption (1.4m, 1.4%)
Super Smash Bros: Super Smash Bros (5.6m, 17.0%), Melee (7.4m, 34.1%), Brawl (13.3m, 13.1%)
Mario Kart and 2D Mario both did extremely well on Wii, but for all of these other franchises and 3D Mario, the attach rate was lower than with previous consoles, substantially so in a few cases. (Donkey Kong is a weird exception where it technically did better than on GCN, but the GCN game was Donkey Konga, so... you know.) The other highest selling games on the console were all Wii Sports, Wii Fit, Wii Play games. The next highest selling games were Just Dance 3, Wii Party, and Mario Party 8, all of which were under 10m and 10%.
So no, I don't think it's unreasonable to say the Wii had a low attach rate for a lot of major franchises.