When this game was on the Wii U for years, it failed to save it from its terrible fate.
Okay, so let me lead you onto this anecdote that I think explains this phenomenon.
In college, I was the person who had the Wii U(I am quite the poor sap). I used to set my console up in my dorms public space, where people would set up their consoles. There was a lot of variety, there was a PS4, there was a Gamecube, there was a modded Wii. And everyone would just go in to play on our game nights, whether or not they were really into games.
A lot of people played Smash, Mariokart, Kirby Airide, Mario Party, that sort of stuff. And guess who's console never got used. People were so turned off by this thing, and it makes sense, because it was an absolute mess for a casual player. Every control scheme was completely different, and unintuitive. For casual gamers, it was a plague that sullied the system. Not to mention how slow, archaic, and awful the system and the OS is in itself. I had Mariokart 8 on Wii U.
Even my best friend at the time, who is now my wife. After a round of the confusing mess of the Wii U, didn't want to play.
Enter the Switch. I got the Switch as close as I possibly could to launch. I got it in April. Coincidentally, with MK8 Deluxe. I set up that Switch in that dorm, and boy did it take up. Everyone was taken aback and wanted to play the "New Mariokart". I don't think anyone realized it was the exact same game I had running on Wii U. And it took off. We would have fun tournaments, kissing bets, all that sort of stuff.
Then, everyone slowly but surely started purchasing Switches, for Mariokart. Soon after, everyone was playing handheld mode instead of split screen on the TV. And just 1 year after the switch released, the Wii and Ps4, and even Gamecube was gone. Because my switch was in the lobby, literally 30 of my neighbors all got Switches.
That's how you know
1. The Wii U was an abomination
2. How great the Switch hardware is, in how appealing it was back then.