>the same government, mysteriously, has no problem building a vast network of roads reaching everywhere and spanning the whole country.

Our road-building has slowed dramatically since the 1980s. The Interstate Highway network would be much more expensive and slow to build today.

>If the US government neglects a section of highway until a city becomes unreachable by roads, there will be riots.

Consider John's Island, South Carolina. The highway that was supposed to go there has been delayed for 33 years. Access to the island/town is through two two-lane roads that get backed up to a standstill every night. There's a running "joke" about how everyone is going to die if there's a major hurricane.