Was it the same flight number? this is not the norm on this flight which i've done many times. However there would be reasons this could happen. You'll always need to get off the plane at big international airports and reboard.Not necessarily the same plane; last time I flew this route (in reverse: SCL-AKL-SYD) aircraft was a 789 to AKL and a 788 AKL-SYD. Had to collect all our cabin stuff and walk to a different gate.
Some see this as an inconvenience, i see it as a rest and stretch, especially in economy. Although I've booked J for later this year, so i might change my mind and find it an inconvenience, although with the better timing of the LATAM flights, reboarding in in Auckland should be dinner then to bed which is good. Awake and arrive around midday the following day.