Technically it and Mario Kart 8 are on the Wii U, but that’s more or less a technicality considering the reality of the situation.
The Wii U was a dead console when Breath of the Wild launched. It’s a Switch exclusive for all intents and purposes.
If it released on another platform, dead or not, then by it's very definition, it's not exclusive.
I take it you don't know what "for all intents and purposes" means.
Mario Kart 8 Deluxe’s features set it leagues ahead of the Wii U version. The portability and vastly superior multiplayer of the 8D make all the difference. While they share much of the same content, the experience is very different for everyone taking advantage of the new content and features. The Wii U version is effectively a mediocre update to Mario Kart Wii. MK8D on Switch is a killer app.
It's the same damn game. Jesus christ.
I guess you had one of those Wii U's that could play the proper battle mode and up to 12 player local multiplayer without split screens :/