Why is the Treaty of Waitangi not considered a legal document?

Question

The Treaty of Waitangi is a founding text in New Zealand, which documents a political agreement signed in 1840 between Captain William Hobson as consul for the British Crown, and a number of Māori chiefs. It is common to refer to it as an agreement which is not a legal document, for example:

In Wikipedia:

The treaty document is an agreement, not a treaty as recognised in international law

In The Guardian:

The Treaty of Waitangi / Te Tiriti o Waitangi – considered New Zealand’s founding document – was signed in 1840 by the British Crown and about 540 Māori chiefs to establish a nation state. While not a legal document, some treaty principles have been developed and included in legislation.

In Cox (2002) - The Treaty of Waitangi and the Relationship Between the Crown and Maori in New Zealand

Orthodox theory holds that the Treaty of Waitangi (“Treaty”) has a socio-political, not legal, force, as it was not a treaty recognized under international law[.]

This is unintuitive to say the least. I can understand that maybe the "Treaty" is misnamed, but it is a formal documented agreement between an agent of the British Crown and local authorities. Why is it not a treaty in the same sense of other colonial agreements such as the British Treaty of Amritsar, or the US Treaty with Creek Indians?

Answer 1

It just so happens that the Parliament is the body to decide what is law and what is not. Being the top authority within the country, it can create or repeal laws as it pleases, grant or take legal power to/from documents.

The reasons why the Parliament does or does not something is politics.

Even if the Parliament wanted to give the Treaty of Waitangi the power of law, it would be simply impracticable because the English and Maori versions of it are not quite consistent (citing the Wikipedia):

As some words in the English treaty did not translate directly into the written Māori language of the time, the Māori text is not an exact translation of the English text, particularly in relation to the meaning of having and ceding sovereignty

Essentially, each party to the agreement had their own vision of what it was. There was no proper meeting of the minds. As a result, the agreement is now a historic document and a political card to play, but not a legal document to be cited directly.