Why wouldn’t they? If NZ decides to withdraw, they’ll be the losers as QF may ramp up NZ domestic Jetstar flights or bring Jetconnect back from the dead which will only affect AirNZ’s domestic revenue. NZ have an ~85% domestic monopoly, and QF is currently supporting their monopoly with this indefinite codeshare. Why would NZ let go of this?
Also, it does benefit plenty of Kiwi travellers who have Canberra, Darwin, Hobart or one of the dozens of regional Australian cities as their final destination. VA don’t fly to most of those smaller cities covered in the QF-NZ codeshare.