TSA requirement to reclear security for all international transits (the logic being that they don't trust the effectiveness of the security check at your departure airport, etc.). So it does not matter which airline is involved; NZ does have a sterile transit lounge at T2 but last I know while that avoided immigration/customs it still required a security check (and confiscation of liquids) at LAX. AKL is nice as you can buy cheap duty free upon arrival (prior to clearing immig/customs).