Its not quite as simple as NZ and Australia , Taiwan is where the losers of the Chinese civil war took refuge, and long-planned to retake mainland at first chance they got. Both the ROC and the PRC still officially claim mainland China and the Taiwan Area as part of their respective territories.
Taiwan aka Republic of China (ROC) , longtime Head Honcho Chiang Kai-shek was preparing to invade mainland China for decades and basically had the same claim of unified China. So just because Chaing's plan didn't work it doesn't mean things changed in regards to territorial unity claims balance just changed now PRC is dominant and claims ROC as part of PRC , while not that long ago ROC claims to PRC were the norm .
Historically, the ROC has required its diplomatic allies to recognise it as the sole legitimate government of "China, but since the 1990s, its policy has changed into actively seeking dual recognition with the People's Republic of China
The other problem , many international organizations Recognised ROC as representative and de facto government of a unified China. So unified China is well used concept.
These are just historical facts unrelated to how anyone feels about ither PRC or ROC