Splatoon says hi.
You see, the problem with thinking like in the OP is that people believe too much in age demographics to truly enjoy themselves. That's
Animation Age Ghetto logic and I vehemently oppose it. A fallback of this kind of thinking may be that Nintendo gets the best marketing output in children and adolescents because they've been conditioned that general appeal games are childish fare. They can't outreach to older gamers because of that instilled logic too.
They've done a great job appealing to older and younger audiences with MK8 and Smash 4 (BestBuy Smashfest exemplifies this in droves.) Then you have Bayonetta 2, Devil's Third, etc., that you can only get with them. Games with hyper violence, sexual content, etc., can be no more mature, or even less, than some games most consider "childish". Gears of War and DOOM create some compelling universes and gameplay scenarios with their gritty directions. Hell, even CoD and Battlefield are taken the same way and they're more tame. But doesn't the appeal of that also crutch on the young kids or the hot-blooded adults who plays the games for that, perhaps because they are insecure about their own maturity? Those low-brow regressions might as well be responsible for the existence of The Guy Game.
The real topic at hand should be why Nintendo isn't pushing for 3rd party support on big multiplats. Sure, they got CoD and most Ubisoft games down. But having big titles like GTAV, Gran Turismo, or even Minecraft makes the baseline of your console more diverse, especially if its made as faithful as the PS4/XBone/PC versions. Nintendo will surely be fine with their exclusive lineup. But they'll yet again miss out on enticing a greater portion of the hardcore gamer because they sleep on 3rd party support.