In the Netherlands, the first country in the world to introduce “gay” ‘marriage’ on 1 April 2001, a Survey by Rutgers World Population Foundation, a centre of expertise on sexual and reproductive health and rights, suggests that about 500,000 people call themselves “gay”. Yet from 1 April 2001 to 2005, only 3% of them married.
So at about 2% of the population, that makes about 3% of 2% which is 0.06%. For New Zealand’s population of 4 million, we should expect (all other things being equal) only 2,400 “gay” marriages in this country. Evidently there are other reasons why the law was changed, but you will have to figure those out.