Sunglasses do seem to be taking the piss more than other items. An expensive pair of leather shoes can easily be justified by the cost of the materials, manual labor, build quality, and extended lifespan over cheaper options.
While sunglasses seem to be a bit of injection moulded plastic with some lenses for a 20x markup.
For most clothing items, there are the luxury name brands, but then there are also affordable options like Uniqlo which sell basically the same thing for a very reasonable price.
For sunglasses, at least in Australia, you get the sunglasses stores that have $200-$400 nice looking sunglasses, and then $30 speed dealer sunnies at the servo. There's nothing in between and no one cloning the name brand styles for cheap.
While sunglasses seem to be a bit of injection moulded plastic with some lenses for a 20x markup.