It's the cause of so many issues in America (physical, mental, social). A great book on the utterly broken build environment in North America is "The Geography of Nowhere":

https://www.goodreads.com/book/show/125313.The_Geography_of_...

Also, people forget - walkable doesn't just mean "somewhere you can walk" - I means you can walk to activities of daily living (groceries, pharmacy, gym, job, friends places, etc).