Why was Australia the main administrator of Naoero during the League of Nations mandate?

Under the League of Nations mandate established in 1920, Naoero was officially placed under the joint authority of Britain, Australia, and New Zealand. While these three nations were the designated responsible authorities, the actual administration of the island was carried out by Australia.1

This arrangement was closely tied to the economic exploitation of the island's resources. The phosphate industry on Naoero was managed by the British Phosphate Commission, which functioned as a joint enterprise between the three governing powers. Australia’s role as the primary administrator allowed for the practical oversight of these operations and the island's governance on behalf of the collective mandate.1