[nukeman]

Likely due to:

- Environmental regulations requiring NEPA analysis or categorical exclusion

- State laws on who can perform road construction

- Construction codes for roadways and bridges

- Miscellaneous overhead for other areas (e.g., Human Resources, accounting, etc)

[MichaelZuo]

Then it seems to be more of a problem with excessive regulation then suburbs themselves.

As a thought experiment, even the wealthiest city in the world couldn't afford a single bridge if regulations required bridges to be made out of stainless steel.