People walk to work when it’s safe to walk. It also has to be possible. Walkability is derived qualitatively and quantitatively. It has to be a safe, pleasant walk and there have to be destinations within proximity.
It also appears that it has to be a place where there is a pedestrian population density that the drivers have to slow down and pay attention. Where there is enough pedestrian infrastructure to support the pedestrian population safely. Where pedestrians get a higher priority than cars.
Except for Detroit, there is a very pretty inverse correlation where the higher the pedestrian population density, the lower the rate of fatalities. Because just like with bikes, there's safety in numbers.