Because American English and New Zealand (and Australia) all derived from British English, obviously, but have drifted less than the accents in Britain. US, NZ, and AUS all drifted differently but the three may still be closer to the British English from the time their colonies were established.
Because American English and New Zealand (and Australia) all derived from British English, obviously, but have drifted less than the accents in Britain. US, NZ, and AUS all drifted differently but the three may still be closer to the British English from the time their colonies were established.
https://www.bbc.com/culture/article/20180207-how-americans-preserved-british-english