Sucks but with so few consoles sold at launch (40k) it's really not that surprising, unless people expected insane attach ratios.
Now, for some numbers:
Zombie U: 12k (not including standalone copies so it's likely more than that.)
Nintendo Land: 24k (again, not including standalone.)
New Super Mario Bros. U: Ended up between Nintendo Land and Zombie U so 12k-24. More than 30% bought it.
We thus know that to get into the Top 10 a game had to do 24k at the absolute minimum. For a Wii U game to get into the Top 10 an attach rate of more than 60% would had been required.
Edit:
The software attach rate was in excess of 2:1 so at least 80k of software was sold, excluding digital software. Total sales for Zombie U + NSMBU + Nintendo Land is 48k at the very minimum leaving less than 32k for the rest of the launch titles.
