Vita can't sell almost 800.000 units before the WiiU sells 2.000.000 units. Vita is reaching its 5th year with only one succesful market. The WiiU, while having poor sales, has a bigger market and more system sellers. The only thing that can change that is a Monster Hunter Vita.
Also, neither of them will reach the 10m this holydays.
EDIT: I know I messed up, Vita appeared in 2011. I was sleepy and wrote a wrong year XD.