Urban Design is Backward - first we build the roads, then we build the Urban area

Except for Brazilia, is there a city where the roadways and land to be occupied were defined prior to urbanization?  

In most cities it seems that they are built ass-backward.   First a tiny town is established and the street lay out is committed.  Population 100.

Then over the next centuries, millions of people are added to the area, and the street lay out makes zero sense and it a huge inefficiency and cost and quality of life diminisher.

The fungus on the dead birch limb in the image above grows out from its central portion in a pattern which maximizes the interstitial surface area - just what cities need - light and air for the inhabitants.

When nature has already shown us by example, why can't we humans get our urban design together?