It's not just a matter of taste, but of waste! I listened to an architecture prof explain why the structure couldn't have been built of glass or plexi: it wouldn't have possible to have those materials at those angles without considerable metal support, which would have ruined the look. Secondarily, transparent panels would have looked like garbage with opaque adhesive holding them together, but the only sufficiently strong transparent or translucent adhesives apparently degrade in direct sunlight! Then there's the matter of the German engineering firm who were supposed to ensure that the joins between the older structure and the crystal were water-tight. As my inside source told me, they procrastinated beginning work and held up the completion of construction before finally admitting that they didn't think it could be done. So, tens of millions of $$$ doesn't buy something that won't leak.