This is a really annoying myth that people keep wanting to believe because "muh Nintendo gimmicks".
Wii's attach rate was very good, and yes these numbers aren't 100%, but it shows a clear enough picture, especially considering number of consoles sold, to highlight that the Wii was a success in every regard. Just Google it or something it's not hard
But yeah, I guess people are still going to insist on being utterly delusional about the ridiculous success of both the DS and Wii to fit some bizarre narrative; where the real "hardcore" market didn't buy into the Nintendo ecosystem thus making it doomed to fail. I hate to break it to everyone, but the hardcore market doesn't actually drive sales. What are the best selling games? FIFA, COD, Minecraft, GTA etc
All casual/mainstream appealing games.
Nothing sells tens of millions or over a hundred million units by catering to some sort of hardcore niche. Now if you're saying Nintendo have made mistakes in their choice of specs/engineering, 3rd party dealings etc etc then that's perfectly valid. However, this weird idea of Nintendo never having real success with the Wii, bad attach rates, and being the "casual" company as opposed to any other company needs to just fucking stop.