Why make Epic Old World if you Demolish it for New World? by Divergent

Why make Epic Old World if you Demolish it for New World?
Divergent
Why would our 1700s and 1800s humanity make amazing epic giant old world perfect buildings across all the nations and different languages with the same style and architecture and type of stone work, if you demolish them afterwards and create an inferior 20th century with ugly buildings and money debt? It does not make any logical sense!