Nobody I know who's moving to the suburbs is doing it to buy a loft apartment and bike everywhere. They're all entering or already in child rearing years and buying houses with yards and cars. As much as people talk about wanting to live in dense walkable neighborhoods, and as much as I wish we could build denser suburbs, the American dream of a lush lawn and big comfortable car is very much alive with millennials.
And more practically, where are you going to build these walkable suburbs? All the prime space of of the inner ring is already built out, and existing "street car suburbs" have already been popular, affluent and expensive for years.