Why is NZ more corrupt?

Radio NZ is reporting:

New Zealand has slipped again, to fourth, in the latest anti-corruption global rankings.

NZ was 1st in 2012 and 2013; 2nd 2014 and now fourth. But no explanation of why is provided.

Maybe NZ stayed the same and Denmark, Sweden and Finland improved?

Here's the site that rates the countries for corruption.

NZ's conglomerate score suffers from a lower ranking in "Rule of Law" measured by another organisation. Here NZ is only 6th of 68 countries.

Additionally, a poorer score from "Sustainable Government Indicators", arising largely from a low ranking on environmental policy it would appear, has added to NZ's drop.

Water management and use and greenhouse-gas emissions have been a focus of policies in recent years. Deforestation has been addressed with an effective permit system. Critics say the government has failed to resist agricultural-industry pressure, but all recent governments have been active in protecting biodiversity.
While New Zealand withdrew from its original commitments under the Kyoto protocol, it is working toward its own independent emissions-reduction goal.

There you go. That's what has contributed to us becoming more corrupt.