A major factor to consider is that the Switch has been able to effectively cannibalize the Wii U, taking some of it’s best games and porting them over. They’re not “new” games, but they might as well be to most system owners. Since the best games on a Nintendo system tend to be 1st party, this has really concentrated their release schedule with some high quality games.
This is how they were able to get Mario Kart, a regular Mario game, and Zelda all out in the same year, as two of those titles are also Wii U games. Splatoon 2 is, by and large, just a slightly upgraded version of it’s Wii U edition. They’ll also drop a Donkey Kong next year, in addition to a new Metroid game, and one of those is a port from the Wii U.
