Mario Kart 8 Deluxe is the new hotness, bringing racing fun to Switch players the world over. With that said, it doesn't mean previous Mario Kart installments are dead. From Nintendo's most recent financial briefing, we know that both Mario Kart 8 on Wii U, and Mario Kart Wii are moving units.
Believe it or not, Mario Kart Wii sold five times more than Mario Kart 8 did in the last fiscal year. Mario Kart Wii went from 37.10 million in March 2018 to 37.20 million in March 2019. Mario Kart 8 went from 8.42 million to 8.44 million. That means Mario Kart 8 sold 20k throughout the year, while Mario Kart Wii sold 100k. Mario Kart Wii moving 100k after this many years shows why Nintendo loves their long-tail sellers!
Just to be 100% clear, this is only about Mario Kart 8 on Wii U, and does not include any sales of Mario Kart 8 Deluxe on Switch.