It’s quite possible that the City planners required the builder to preserve the windows of the now demolished building. I am sure that the cost of working around the architectural feature is more than starting from scratch with a blank sheet.
You see a lot of this in London. A building is gutted and all that is left is the facade that faces the street. A couple of years later, when the project is complete, you see the ‘original’ building preserved, or apparently so.