What makes no sense is leaving tons of money on the table that would also please a majority of the fanbase. I don't think Nintendo is going to ignore the fact that far more fans like Mario Kart than any other racer just cause a port already exist on the system. A 20+ million seller like MK9, even if it were to cut MK8D's legs to 0 (lol no), would still net a lot more profit than the 2-3 million sales Diddy Kong/F-Zero/Kirby Air Ride would generate. From both a consumer and business standpoint, MK9 should hold more priority than most other games let alone just racers.
I've read a rumor that Nintendo is strongly considering to delay Breath of the Wild 2 until 2025 because the first game is still selling so well.
I've also read another rumor that stated that Animal Crossing and the remake of Xenoblade Chronicles are the last first party releases in 2020 because there's no reason to release any more new games when so many of the old ones are still doing so well.