Careful: Chicago is a big city, and it's tough to characterize population loss the way you are. The neighborhood that experienced the most population loss over the last 20 years was Auburn-Gresham, which, while "walkable", is not a place a lot of Chicago residents go out of their way to walk in. One large pattern of population shifts in Chicagoland is from the formerly-redlined south and west sides to the south suburbs, or to the southern states.

The parts of Chicago you'd think about when you think "walkable cities" are thriving.