Fair point. It also looks like the structures act as waveguides. Making a 570nm waveguide will be more difficult than a 1400nm waveguide.
On a slightly different note, these things somewhat remind me of a Fresnel.
Yes, except with much small features, so they rely on diffraction instead of refraction. I think they're basically a computed hologram of a convex lens, but somehow made to work with non-coherent broadband light.