Updated
Most people won't buy sunglasses without seeing them on a face, and online they can't try them on. The photos have to stand in for the mirror: how wide the frame is against a face, where it sits on the nose, how dark the lens really is.
Eyewear ranges are also wide. One frame shape comes in several acetates and lens tints, and every combination needs the same angles. Lenses reflect everything, so keeping that look consistent across the range is most of the work.