Seems like simpler fabrication but not sure why they can't just make a master and then stamp/pattern these at scale like how gratings are manufactured.
you definitely can and people definitely do this. There are arguments that stamp patterning is better suited for optics as well - specifically point defects seem to be less deleterious and that the feature shapes (not sizes) are more readily done via stamps. However, typically a lot of semiconductor manufacturing is viewed from an electronics perspective today, where stamping is definitely considered an inferior process.
