As explained above there are a number of reasons listed above.

For reference economy stretch hasn't taken away any existing seats - media made a shambles of this story after an incredibly poor Stuff article which was actually totally wrong. Despite Stuff's claim that nothing actually changed with the seating, the 77W seating was reconfigured as the planes underwent maintenance last year and this year. The Skycouch row that was in this forward cabin was swapped with seats in the rear cabin (so no loss of total Skycouch rows) and the remaining seats in that cabin were reconfigured for the extra pitch.