Making a strong square frame is notoriously hard. If anything is slightly out of alignment, it readily collapses. Unlike walls that can have a hidden truss for added structural integrity, windows need to remain open. So, why do most modern buildings have square windows? Even if they were just slightly trapezoidal, they'd be much stronger. The Incans seemed to understand this; none of the windows at Macchu Picchu are square. And, despite heavy seismic activity, the window frames remain intact.
Have we stuck to square windows because they're easier to measure? Or because they make more efficient use of glass? I wonder whether these short-term cost savings make sense in the long-term when they add structural limitations. In boats, airplanes, and cars, we know that square windows are suboptimal. Maybe it's time for this logic to be extended to buildings.