Large areas of American suburban development have no continuous pedestrian route between houses and the nearest shop. The absence was written into the rules that produced those neighbourhoods.
Subdivision rules made sidewalks optional
Local ordinances governing new residential development set requirements for road widths, drainage, setbacks and lot sizes, and in many places treated footways as discretionary.
Developers pay for infrastructure and pass the cost into house prices, so anything not required is a cost that can be avoided while competitors avoid it too.
Where the requirement was absent, the sidewalk was absent, and the pattern repeated across thousands of separate approvals.
The street was designed for a different user
Post-war road standards prioritised vehicle movement and emergency access, producing wide curving streets with generous turning radii.
Those geometries encourage higher speeds and lengthen crossings, which makes walking less pleasant and less safe, and lower pedestrian numbers then justify not building for them.
Curving layouts with cul-de-sacs also lengthen every journey. Two houses a short distance apart as the crow flies may be a considerable walk by road.
Separated land uses put destinations out of range
Zoning that divides residential, commercial and industrial areas means the nearest shop is often on an arterial road rather than at the end of the street.
A walk that would take a few minutes in a mixed neighbourhood becomes a long trip alongside fast traffic, so the car is used even for small errands.
Once nearly every household drives, the political constituency for pedestrian spending is small and diffuse.
Maintenance liability sits awkwardly
In many jurisdictions the adjoining property owner is responsible for repairing and clearing the footway, and may face liability if someone is injured on it.
That converts a public amenity into a private obligation, and homeowners have reason to resist installation on their frontage.
Gaps result. A route that is paved for three blocks and disappears for one is unusable for a wheelchair or a pushchair, which makes partial provision close to worthless.
Retrofitting costs far more than building first
Adding a footway later means acquiring or asserting rights over land, moving utility poles, rebuilding drainage and often regrading front gardens.
Accessibility standards apply to new work, so a retrofit must include ramps and crossings that add to the price of each block.
Municipalities facing that bill tend to prioritise routes to schools and transit stops, which is sensible triage and leaves most streets unchanged.