Because the sprawl has become an emergent phenomena that is self reinforcing.

Are you familiar with conway's game of life?

What we have produced is a system of urbanization that, in a sense, behaves like a fire. Our cities don't properly increase in average density and land value in a smooth transition like you see in Europe and Asia. Instead, they're burning outwards leaving a growing circle of rot behind them.

You can create "fire" patterns in conway's game of life that take pristine space, and leave behind low density wreckage as the wave burns through. That's what I think we have created. There is no countervailing force to arrest the successive growth of rings around the burned out core.

To put it another way, our cities are growing like this...

Because the sprawl has become an emergent phenomena that is self reinforcing.

Are you familiar with conway's game of life?

What we have produced is a system of urbanization that, in a sense, behaves like a fire. Our cities don't properly increase in average density and land value in a smooth transition like you see in Europe and Asia. Instead, they're burning outwards leaving a growing circle of rot behind them.

You can create "fire" patterns in conway's game of life that take pristine space, and leave behind low density wreckage as the wave burns through. That's what I think we have created. There is no countervailing force to arrest the successive growth of rings around the burned out core.