I dont think there is much money on playing NZ domestic league.
Any money to be made is from being in the national team.
So, if you are not so sure about your prospect in being the contracted 15 or so players, County cricket gives a much better financial security.
Too bad for NZ. they are also loosing some good players.
Verily, in the remembrance of Allah do hearts find rest [Al-Qur'an,13:28]