More practical than changing Atlanta to some imaginary car-free utopia. But perhaps the advantages of living in a car-free city aren't that great after all?
Or the pros/cons don't stack up to a net difference that is big enough to be worth relocating over.
The point is: for some reason these cities don't suddenly become so liveable that they're a huge success, neither economically nor as a destination for tourism or retirement. Perhaps those who have discovered their love for this fantasy haven't really thought about all the consequences.
Atlanta is already changing to a "car-free utopia" that you're dismissing. Many neighborhoods around Midtown, Inman Park, and several MARTA stations are both more walkable and in enormously higher demand than 20 years ago.