Their existence is far more constant than heavily urbanized areas.

Certainly not. Moderately urbanized areas are a historical footnote. They came into existence less than a century ago, with the emergence of automobilism and cheap fuel.

Heavily urbanized areas have existed for millenia.

This is highly unrealistic. Most people do not want to be packed in tighter with other people, they want more space not less.

The alternative is that they stop existing altogether when personal automobiles become too expensive for the average consumer to own and operate.