Nintendo actually has marketed heavily towards parents this gen. The last 2-3 holiday seasons for Wii U were basically TV marketing centered entirely towards parents buying the machine for their family. There's even a freaking line of commercials where the kid is explaining to their parent why they need a Wii U.
In actuality, Nintendo is dead off with this type of marketing. What drove the original Wii is aside from usual mix of Nintendo lifers and family console people that Nintendo always gets, the Wii brought in ADULTS who wanted to play Wii Sports, Wii Fit, and just a little touch of Mario for nostalgia sake
The GameCube and Wii U do not connect with the general adult gaming population at all. They don't have a Wii Sports type break out and cater almost entirely to Nintendo fanatics and the small group of parents who want something for their 6-10 year old, but don't want it to be too violent. The N64 had GoldenEye at least that somewhat filled that role.
Nintendo Land also made a key deadly sin in becoming too cartoony/stylized. Wii Sports worked precisely *because* it wasn't Mario Sports. The graphics were simple, the characters regular humans (better yet just avatar representations of the person playing). You make the game too cartoony and you turn off the adults and make them self concious about playing a "kids game". Nintendo totally missed that too. Wii Sports doesn't work nearly as well as Mario Sports, nor does Brain Training work as Mario's Math Studio.
Nintendo Land doesn't even feel like a real theme park, it just feels like some wacky place out a cartoon, another poor design choice. Without appeal to adults a Nintendo console just invariably becomes stereotyped as a "kids toy", and kids don't even choose Nintendo overwhelmingly. Some kids like Batman more than Mario (a lot actually). A lot of kids like playing soccer or hockey or football or basketball ... guess which console they would prefer. By sixth grade kids, especially boys become fixated on whatever it is the older kids are doing too.