What are you talking about? New Zealand is not part of Australia. We have completely different laws and a proper R18 rating. I can understand why the publisher might source boxed retail copies from Australia since bringing over an uncensored batch from elsewhere would push up transportation costs, but for digital distribution this isn't acceptable.
It's likely AU and NZ have similar territorial and contractual agreements with their distributors. You should understand studio != publisher. Sometimes, it's out of their hands.
What would GoG/CDProjekt have to gain by pissing their customers off like this? Nothing. I am 100% sure they're unhappy about having to deliver a censored product to AU, and a pricier game for their Oceanic customers.
They have to do it out of legal obligations or possible repercussions, like distribution rings threatening to sue because they can't gouge their local customers the same if there is a cheaper alternative out there. In which case GoG and Atari might lose the entire market if it goes to court.
I don't know the specifics, but often, publishers are responsible for these decisions, and since publishers will give some money to studios to develop the game in exchange for distributing it, and because CDProjekt is a small studio and is unlikely to have the leverage of the bigger ones in such decisions (the studio that developed Divinity II went through this as well), you need to show more understanding of the underlying issue.
There are EASY workarounds if you're willing to be just a little resourceful.