Well also building cheaper makes converting such structures to other uses more costly too. You can't simply start notching steel and adding more features and beams without a complicated engineering review because those beam were so carefully designed as to just barely hold up under their original plan.

You can't simply add a second story to a mall or walmart or modern school, none of its main structural pillars or beams could hold it. But with an overbuilt structure from 500+ years ago you likely could add another floor or two with minimal improvements to the base structure.