Road networks can only work in dense environments. You think that building and maintaining expensive transit infrastructure can be done outside of large cities? Last mile transportation means that we couldn't build out roads to people's houses. Relying on car transport would require parking your car in the main city square and walking home from there. Not to mention that car transport is universally less efficient in energy to get from point A to point B.
Road networks can only work in dense environments. You think that building and maintaining expensive transit infrastructure can be done outside of large cities? Last mile transportation means that we couldn't build out roads to people's houses. Relying on car transport would require parking your car in the main city square and walking home from there. Not to mention that car transport is universally less efficient in energy to get from point A to point B.