The issue that Nintendo sees with that - as well as other companies - is the one and done method leads to less discussion.
I'm going to use TV because thats an easy frame of reference for me. Netflix always drops their content with the full season at a time. Many people binge it - so theres a bunch of articles all at once, and discussion, and then...2 weeks later, its done. No more discussion (AKA free advertising). Compared to a weekly release - every week theres articles about that episode, and whats next. And people message their friends, and talk at work, etc etc. "Did you see what happened? Whats gonna happen next week?" etc etc. Often viewing numbers go up every week as people tell their friends to tune in or people want to know what everyone is talking about.
(Obviously Netflix prefers their all-at-once model, but its a big debate between consumers who prefer to binge on their schedule and the fact that most of the other streamers do weekly releases (Hulu, Amazon Prime, etc.)
Its the same with video games. Every time Animal Crossing does an update, Polygon and Kotaku and AnimalCrossingWorld etc etc etc write articles and people text their friends about the new things and post on Instagram with new features...Free advertising. With games, it also has a few other benefits - longer to work on specific features and player feedback on what they like/is important to them (like the changes to the Bunny day spawn rates).
Business is a tug of war between what is best for the consumer and what is best for the company. You may not want your experience to be effected by Nintendo (and most companies) wanting free advertising...but thats how big companies work nowadays.