I have put a great deal of thought into this.
CLEARLY Nintendo sees the backlash. They see the dislikes on any video related to it. They must see the minuscule amount of people who use the app. They don't have their heads buried in the sand. They know gamers are dissatisfied.
I actually think there is a much more nebulous reason for it all - they simply don't give a fuck. They never really valued online play in the sense of social functions, parties, and communities. Nintendo sees social gaming as a local experience. They have literally been dragged into the online race kicking and screaming. They don't want to do it. Their focus is on local play. On families. On being with friends. On being in real-life. They really, really value this aspect of their brand. It is reflected in nearly ALL of their marketing and promotional materials. They view a heavily networked experience to be an isolating one, and the image of a gamer playing by himself/herself with a headset is considered so anti-brand to them, they nearly see it as toxic and damaging.
This is why they not only put very little budget and effort into their online infrastructure, they actively try to limit it. They have stripped back features from the WiiU and 3DS. They have re-introduced Friend Codes. They have released a modern console without blue-tooth support.
Nintendo actively supports local multiplayer and actively limits online play. It goes along with their branding. It's a terrible strategy if you ask me, but their bread-and-butter is kids and families and they know it. They know the 'good enough' online is fine for us. Smash Bros Ultimate sold 5 million copies in one day and Mario Kart 8 Deluxe is north of 10 million. I have fun with the online in these games. It works. The netcode works for me. However I wish I could make parties, join friends, send invites, voice chat easily, get into deep strategies in Splatoon, laugh and make friends in Smash Bros. I have accepted it ain't happening. I still love em'. I still love the games.
And as a 31 year old Nintendo fan who has had every one of their consoles, I have said it before and I'll say it again about Nintendo getting online right : "maybe next gen?"