It's not that the title wasn't aligned with the userbase (that's a myth), it's that the title was niche genre, had a completely uninspired name, was a little bit shy on quality and the userbase was tiny. The attach rate is well over 10%, which is outstanding, but there are so few systems out there. Games are so expensive now that it's impossible to make money on an exclusive game on a new system in the first year, unless you're possibly the top game.
If ZombiU had a title like "The Last of Us", it would have captured imaginations much better. It also needed more impressive visuals for a next-gen title, not just good visuals. It was also really strictly in the hardcore zombie survival genre, which is a tough sell for a lot of people, including me. I haven't bought it (yet), but if it was more like a zombi/survival/character-driven adventure like The Last of Us impresses me, then I would have bought it day 1.
Still, a half mil on the Wii U is nothing to sniff at. Expecting much more - even if the Wii U was selling much better - is a bit naive.