Problem here is:
The Vita is competing with the 3DS. 3DS is likely to sell 80m-100m and does not take much software from the Vita. Both have a lot of exclusives from certain companies.
The wii u is competing with the PS4 and the XB1. Both may sell 100m+ and 70m respectively and makes the wii u devoid of any 3rd party support.
Relatively it is harder for the wii u to compete especially since with the Vita-3DS situation you either buy the 3DS or you buy the Vita. while in the PS4-XB1-wii u situation you either buy the PS4 or you buy the XB1. (and maybe wii u on the side) MS is probably pretty happy that the PS4 is close to XB1 in power, otherwise it may have even sold worse then the wii u.