Animal Crossing: New Horizons has been an incredible success for Nintendo, selling 13.41 million copies since launch and landing high in the system's all-time top seller list. There are numerous factors involved here, but one element that is perhaps leading to a surge in sales is the current state of the world and the COVID-19 pandemic--which might also be why the latest Animal Crossing has had strong digital sales.
According to Nintendo's recent investor call, live-tweeted (and translated) by Astris Advisory Japan KK's Dave Gibson, about 50% of Animal Crossing: New Horizon's sales were digital, with people buying the game through the Eshop in lieu of picking up a cartridge from a store.
Nintendo is expecting a growth in digital sales within the next financial year overall, but not that all games will hit a 50-50 split--the Switch's low internal memory and the cost of SD cards means that many people prefer to own their games physically.
AC sales were about 50% download. Digital was high in 4Q, dont assume this level will continue but for FY it will grow
— David Gibson (@gibbogame) May 7, 2020
Animal Crossing is also a game that players will likely keep returning to, or want to jump into briefly every day over months or years, which makes a digital copy attractive.
Animal Crossing: New Horizons received a 9/10 in GameSpot's review. "New Horizons certainly came at the right time, and its strengths are particularly comforting right now," reviewer Kallie Plagge wrote. "I'm as excited to see what random events await me each morning as I am glad to have it during hard times, and that's sure to keep me coming back for the foreseeable future."