Because it's New Zealandese.
Because it's New Zealandese. The New Zealand language. When you go to Japan (never been there) you must either learn basic Japanese, get an interpreter or talk exclusively with a few people who have learned English as a second language. But because of colonialism and imperialism, not even New Zealanders need to speak Māori on a daily basis beyond a few basic words that have diffused into New Zealand English. English will be an important language for international business for as long as New Zealand is a Western country, but within Aotearoa there should be visible signs of Māori culture and language throughout the country to the point that virtually everyone who stays here will acquire basic knowledge of te reo Māori and tikanga simply because it's all around them.