Just making a game cartoony and thinking it'll sell to the Nintendo fanbase "just cuz" doesn't really make sense.

If that was the case Wonderful 101 would've sold a lot, so would DKC: TF, so would Codename: STEAM, and Metroid Prime Chibi Force would be a shoe in for big sales.

LEGO Star Wars sold great, but LEGO and Star Wars goes together like peanut butter and jelly. Those are two huge brands coming together and it was before LEGO made too many licensed spin-offs, so it was catching that trend at the rise. 

wonderfull 101 isnt a AAA title.

Donkey Kong isnt either. Its a 2d plattformer and sold pretty good for that (compare it to rayman legends).

I talk about big AAA games like Assassins creed.

Make them worth getting and people will buy them

No. Look ad Bayonetta 2´s sales. That was worth getting right? The wii u owners just dont care about those games. Even a Assasssins Creed port that get all dlcs, run in 60 fps and ps4 graphics on wii u wont sell more then 600k.

thats wyh many kids do own the system and their parents wont buy them rated m games.

Thats why adults who own a wii u are only a few nintendo fans and they do own a pc/ps4 or xbox one. It doesnt matter how good these games are made.

Make them appealing to the wii u audience. 

what are the sales now? How long has it been out and compare that to the two other platforms. The game is still full price while the first game sold better thanks to being longer on the market as well as ending up in the bargain bin. I still haven't bought my copy yet but planning on getting soon as it is worth it. AssCreed and most other turd parties are not

The cell shaded idea is very good. Also; bring something different in game modes (Bowser/DK Amiibo on Skylander or the Arcade mode like in Medal of Honor Heroes for the Wii), more and/or better marketing (look Splatoon, is a new IP). You made a great example with those images using Assasin's Creed.

its at 600-700k.

It is 27€ on amazon in grmany. Full priece=

The game is frequently on sale for 10-15€ on local stores.

It was the 2nd best rated game on metacritic in 2014 (first was smash).

There is no audience on wii u for those games. Even if they are almost perfect.

+keep in mind that many people bought a wii u just for that game. Thats game wasnt bought by the majority of the wii u´s audience. Those people will get every multiplattform on their pc/ps4/xbox one.

In addition games like Mass effect 3, need for speed most wanted U and deus Ex human revolution where very good ports. Still sold very bad (between 0,09 and 0,22mio).

These are just wild guesses, perhaps its 90% kids/10% nintendo fans or 10% kids/90% nintendo fans or any other share between. And correlation does not imply causation... the fact that Mario Kart 8, Super Mario 3D World, New Super Mario Bros. and Wind Waker HD have great sales and "cartoony graphic" doesn't proof that the cartoony look is the most important factor for the great sales. Maybe they sell great because they have great gameplay or because Mario and Zelda games get great reviews or because Mario and Zelda games have a great reputation or because Nintendo was advertising the heck out of them... or a combination of all these reasons.

So please explain why Bayonetta 2, Assassins Creed 4, Need for Speed Most Wanted U, Mass Effect 3 and much more didnt sold good. They good gret reviews too. And special bayo2 is exclusive to wii u.

I agree that its not "the only reason". But its a very very big reason (in my opinion). The best selling realstic looking game is zombi u which sold 800k and even got a bundle. So the cartoony graphics do have a big part in terms if sucsess of an game.