Because of the fact that every Kiwi and his sheep are moving over here to find work and a better life. If we had the same government, then it wouldn't be such a problem. Where I live, us locals (who are born and bread on the Gold Coast) sometimes like to play the game called "spot the local"
That's fine by the loyalists amoungst us over here. It increases the average IQ of both countries
But seriously, good on those that want to get the BIG MONEY in Oz, it creates shortages in some industries here and in turn that makes those sectors more profitable for the ones that stay. It's win win.