I don't think its hard to work out why mature games fail on wii u;
There are probably 3 main reasons;
1. Many wii u owners will be families or young gamers who won't get/be allowed mature games
2. Many wii u owners love mature games but also have other systems (like me) and will buy them for more capable consoles/hardware
3. Many gamers are only interested in mature games (they wouldn't have bought a wii u in the first place)
So your only chance of selling mature games is really gamers like me in the second zone but they need to be exclusive or at least very special editions that warrant purchase over technically more proficient versions maybe extra levels, great gamepad support etc.
However the userbase is too small and gamers like myself may only make up a small percentage of wii u owners. It may be casual young/family gamers make up 80% of the install base. I don't know the figures but of the 7 million install base may be there is only a maximum 1-2 million gamers interested in wii u mature content.
