Back then they didn't know what the Wii U's fate was.
Black Ops II was on Wii U though, as was Ghosts.
In fact Treyarch made the Wii U version of Ghosts. Though IW made the other versions.
75% chance BO 3 will come to Wii U.
Added some stuff. Ghosts was 2013.
Though I'm gonna lower that optimistic guess.