Why are coalition governments so common in New Zealand?

The country's MMP electoral system was designed to give more diverse voices entry to parliament

Coalition governments - regarded with horror in many other democracies - have become the norm in New Zealand since the country shifted to the MMP electoral system in 1996, ditching the British first past the post" system.

MMP - mixed-member proportional - was designed to allow more diverse voices entry to parliament, and award more power to smaller parties in an attempt to dilute the hold that the Labour and National parties had on government.