>>5700922I'd change that question a bit: why don't more companies with a faceplate system actually offer different faceplates to buy?
Even the ones that do have such a system usually only have one, maybe two faceplates to offer for one sculpt (open eyed and sleeping version).
I agree with other anon though, it's harder to make such a system (no matter if it's a half face/half back one like Unoas have, or one where the face part is a lot bigger, like with Granado).
But if you already made a working one, why not add some more face options?