That seems overly broad - a surviving old city tourist area might be well preserved but elsewhere, post-war city rebuilding programs were cheap, rushed and ugly

That seems overly broad - a surviving old city tourist area might be well preserved but elsewhere, post-war city rebuilding programs were cheap, rushed and ugly. Even later development is unloved because "high-design" of the time was infected by Brutalism. These already troubled urban centres were then hollowed-out by economic troubles in the 70s leading to areas of dereliction. Over the past few decades, urban regeneration programs have been widespread to remove the bleak post-war prefab concrete monstrosities. Unfortunately what is replacing them is cheap and uninspired compared to pre-1900 architecture so I can't see us valuing it that much in 100 years.