Nintendo honestly hasn't been able to sell consoles very well for like 15 years now aside from the motion gaming craze which kinda fizzled out after about 4 years. So 11/15 years they've struggled to sell home consoles.
Their consoles are just seen as too much of a "for kids" product, and even kids don't want that (they want the games their older brother/cousin/kid down the street is playing). The "wholesome fun for the whole family!" thing from the 1980s that Nintendo keeps sticking to just doesn't resonate today and really hasn't for a while.
The industry in general has moved more towards violent/dark Western software too ... look at any monthly NPD ... 90% of the top 10 is pretty much exclusively that type of game or a sports game every single month.