At 30 and playing for a semi pro club he might be establishing a career outside of football and have a good job, etc.
If he is interested in Australian citizenship and all that comes with it then under the new regulations for New Zealanders he needs to have a certain number of years of continuous residency in Australia while earning an income. His decision not to come to the Nix may be as simple as that.
"New Zealand citizens can apply for Australian citizenship by meeting general residency requirements, as time on their Special Category Visa (SCV) counts as permanent residence for citizenship purposes from July 1, 2023. You must reside in Australia for four years on a valid visa, hold an SCV for the final 12 months, and have been absent for no more than 90 days in the last 12 months and 365 days in the four-year period. You also need to pass a character assessment, and most applicants must pass the Australian citizenship test and demonstrate a basic understanding of English." (from HomeAffairs.gov.au)