Thanks for the clarification - I had forgotten Aviation Security was a different agency.

Some of the commenters already point out though that there is space for more scanners/xrays/whatever, just that "the airport" hasn't installed more - when it's not their job to do so (at least I believe it isn't - I know in US airports, many of those are actually airport assets rather than DHS/TSA assets but I'm fairly sure in NZ the government owns them)