They do have an unfortunate habit of leaving the first half of the year devoid of system sellers, though they seem to have learned as next year Animal Crossing is hitting in March.
What you call a habit is actually an exception. Between the four years 2017, 2018, 2019 and 2020, the only year that had no system seller in its first half is 2018. And no, I am not cheating with 2019 because I count Super Mario Maker 2 due to its June 28th release, because one game you have a habit of shoving out of the way (New Super Mario Bros. U Deluxe) is a system seller. NSMBU Deluxe is #10 on Switch's LTD chart, but it's actually the ninth-best-selling Switch game in the USA because NPD has the illogical habit of counting Pokémon versions as entirely different games.
That doesn't mean that Nintendo can't do better in the first half of the year, but merely that your assertion is wrong.