Alright, let's settle this. Nintendo caters to third parties; they just don't cater to the same third parties as Microsoft and Sony. Likewise, third-party games sell well on Nintendo consoles; just not the same third-party games as the ones that sell on Microsoft and Sony consoles.
Let's look at the Black Ops II example, without outright assigning blame to anyone, because that will get us nowhere (it will get us 21 pages deep into nowhere to be specific).
So, who owns a Wii U? To answer this we have to look at the video game market as a whole. Many people own multiple consoles. Many Wii owners own either a PS3 or a 360, or both. The percentage of Wii owners who owned another 7th-gen console likely increased throughout the gen, especially in the last couple of years as Wii support faded. Now, where are Call of Duty fans? There were a decent number on the Wii at the start of the gen, but as time passed, Wii COD sales declined and PS3 & 360 COD sales grew. Perhaps this reflects the Wii owners who, between COD releases, bought another console and decided to start playing COD on that console, instead. There were a number of reasons to make this change.
Now, who has bought a Wii U so far? More to the point, why would anyone buy a Wii U right now? Very few gamers will buy a Wii U for Call of Duty; if you are a COD fan, you must already own a console on which you play COD. Presently the biggest reason to buy a Wii U is New Super Mario Bros. You may buy one for Nintendo Land, or for ZombiU, or in anticipation of a future release, but for now let's go with Mario.
If Mario fans are the only people buying a Wii U right now, because Mario is currently the only reason to buy a Wii U, then the potential sales of Call of Duty on Wii U are limited to the number of people who play both Mario and Call of Duty. Or, more accurately, they are limited to the percentage of Mario fans who play Call of Duty multiplied by the number of people who have bought a Wii U -- because not all 20 million+ Mario fans have bought a Wii U already.
We can guess that this leaves us with a very small potential audience for Call of Duty on Wii U -- presently. There are two ways to remedy this: Nintendo can make exclusive games or deals to convince Call of Duty fans to migrate to Wii U. This is a risky move that might not work, might not benefit Nintendo at all.
The other potential remedy is for Activision to market their game better, to convert current Wii U owners into potential customers interested in Call of Duty. You know, convince people to take an interest in and buy your game. Build a fanbase the old fashioned way. Activision has basically stepped back over 10 years to a time when the masses didn't care about Call of Duty, and they didn't know how to react to the fact that their game isn't selling itself on its name alone in this instance.
I'm not "blaming" Activision for Call of Duty's low sales. Just saying they should have expected this -- and that at this juncture, they can either complain about it, or take steps to fix it. Nintendo can also take steps, but they are not obligated to, and they may not be willing to, and their "fix" would be a temporary one at best and an utter failure at worst. The fate of Call of Duty sales on Nintendo consoles is in Activision's hands, where it belongs.