This article by Healthline explains thoroughly how and why Animal Crossing is so great for mental health and well-being. Key points:
"...When our collective mental health is languishing, it’s even more important that we still have goals - even if those goals involve building a pretend bridge. Putting a stake in the ground gives us momentum that we might otherwise lack. It can be as simple as mastering a new craft or hobby, as silly as renovating our virtual homes on “Animal Crossing,” or as ambitious as a promotion at work.
These goal-driven behaviors help contribute to our sense of purpose, fortifying our mental health even in lockdown. I believe that’s why a game like “Animal Crossing” can be a source of comfort - especially when the world seems to have come to a screeching halt. It gives us goals without overwhelming us; it offers a sense of connection and novelty that our brains thrive on."