It's because of Heads mainly. Three seamers and two spinners definitely works better on most pitches than four seamers and one spinner, so NZ's main two balance options at the start of the season with Smith+Dorn or Ritchie+Heads. The latter won out.
Code: New Zealand 1st Innings JJD Heads b James 0 1 0 0 S Bakkum ct Delonge b James 7 14 0 0 SM Morgan ct Taylor b Pimpkins 49 81 6 1 J Torres lbw b Rask 11 16 0 0 ML Martyn not out 172 272 15 4 JD Hurricane ct Boland b Rask 32 81 0 1 DP Howell ct James b Emm 28 64 2 0 GJ Weaver ct Boland b Rask 21 31 1 0 HJ Bots ct Hughes b Emm 15 33 3 0 HT Davis lbw b Taylor 20 15 4 0 JJ Ritchie b Taylor 14 10 3 0 Extras (byes 0 leg byes 10 no balls 9 wides 1) 20 Total (10 Wkts 101.3 Overs) 389 Fall of Wkts 0 18 53 97 180 261 309 346 375 389 James 21 3 67 2 6 0 Rask 23 3 86 3 2 1 Pimpkins 7 0 41 1 1 0 Taylor 20.3 1 83 2 0 0 Emm 23 1 77 2 0 0 Speirs 5 1 12 0 0 0 Hughes 2 0 13 0 0 0
Code: NSW Country 1st Innings DG Speirs not out 112 190 12 1 DN Boland b Davis 0 5 0 0 T Delonge lbw b Davis 14 23 3 0 BG Herd ct Torres b Davis 0 1 0 0 JB Dempsey ct Torres b Weaver 25 28 4 0 A Pimpkins ct Howell b Heads 15 21 1 1 JM Hughes b Ritchie 16 24 3 0 KN Rask ct Weaver b Ritchie 0 1 0 0 BJ Taylor ct Bakkum b Davis 20 46 2 0 AJ James ct Howell b Bots 8 19 1 0 HG Emm ct Hurricane b Bots 0 2 0 0 Extras (byes 0 leg byes 4 no balls 2 wides 1) 7 Total (10 Wkts 59.4 Overs) 217 Fall of Wkts 13 40 40 82 109 140 140 203 217 217 Davis 17 1 68 4 0 0 Weaver 11 2 41 1 1 0 Heads 10 3 26 1 1 0 Bots 8.4 0 25 2 0 0 Ritchie 13 0 53 2 0 1 New Zealand lead by 172 runs on first innings.