I'm pretty sure the CoD ports outsold almost all the wii exclusive shooters by a wide margin. I think Red Steel broke a million too, but that game disappointed everybody so hard that the completely-unrelated and much better sequel never got a fair chance to salvage things due to the toxic brand name. CoD WAS the successful wii shooter. It just got drowned out by the sheer scale of the brand's popularity elsewhere.
Then there was the RE4 port, I guess.
Many people owned a Wii next to their PS3 or Xb360. Combine that with the curiosity of FPS motion controls and it was no surprise the CoD games sold pretty well.
This generation the Wii U has struggled a lot right from the start, so many people who played those games may have not jumped on the Wii U bandwagon yet. Sales of the Wii U have only recently improved (and will very likely improve in the coming months and in 2015 when more of the must have titles come out).
Cod on Wii sold 1 or 2 million in total in an install base of 100 million. In 2013, when Cod Blobs2 and Ghosts game out, the Wii U was at 5 million, so those games abvously didn't sell well. I don't even knwo what Ubisoft is expecting. Wii U only gets 3rd Party ports, which just seem to not excite Wii U owners.
It was very unfortunate that Red Steel turned out so shitty. Ubisoft had a great chance to establish an new, Nintendo exclusive IP on their systems, which they could have made a successfull series out off, but it didn't happen. At least Ubisoft tried, although they could have maybe used a bit more recources to make Red Stell 1 a success.