I just think they tried to play it super safe... The Wii heavily(!) catered towards casual and non-gamers, and because of that sold like crazy, but many people and/or Nintendo fans still screamed for a new „hardcore“ Nintendo console, catering to them. And the WiiU arguably was exactly that, but frankly not much more!
Not saying anything about these games quality, but...
Can all be classified as "original game on another console sold well, let’s just do the same thing again for hopefully secured success“...
Now I would agree with OP‘s assessment that these games are niche or too specific, for me it really just feels like Nintendo wanting to tread old ground, play it safe, and yes, pander to their core fans! The games are pretty good, but the ones mentioned above are a little too... un-creative.
With not even two years gone, look at the Switch:
BotW, arguably the best, but at least the wildest, most creative and different Zelda in years
Odyssey, a Return to the sandbox-y style of Mario, like in 64 or Sunshine, plus a new "gadget“/power, that changes soo much
M+R: Kingdom Battle, a pretty out of nowhere and super creative collaboration with Ubisoft (to a lesser but still awesome degree, one could also mention Starlink)
Classics that never(!) were on a Nintendo console, like Skyrim, Doom, Wolfenstein, La Noire or the upcoming Final Fantasy games
Those alone are just so much more... adventurous, if you know what I mean, it’s great!