Wikipedia seem to imply that it's because the Women's Oceanian Nations Cup is being used as qualifiers for the Women's World Cup, which New Zealand qualify automatically for as host country.

Has the Championship of an entire continent got no value in itself? It didn't stop Australia playing in the Women's Asian Nations Cup!

What about the players and fans of New Zealand, who are now deprived of the opportunity to win a major trophy? What about people like me who had tipped New Zealand to win it?

What's it going to do for the prestige of the Oceanian Nations Cup if the best team in Oceania isn't even playing in it?!

This is insane!
--- SBBSecho 3.06-Win32
* Origin: SportNet Gateway Site (24:150/2)