Why is the Govt going slow on drug driving testing?

The Herald reports:

Families who have lost loved ones to drugged drivers came together at Parliament today to ask the Government to hurry up and introduce roadside saliva testing for drugs.
Among them were the families of Ian Porteous, 80, his wife Rosalie, 76, his sister Ora Keene, 84, and friend Brenda Williams, 79.
The four died in a head-on crash with Jeremy Thompson, 28, his 8-week-old daughter Shady and Nivek Madams, the 8-year-old daughter of Thompson’s partner Ani Nohinohi.
Nohinohi was the sole survivor of the crash at Waverley in Taranaki in June last year.
A coroner’s inquest last week into the Waverley crash, at the time one of the country’s worst, was told that Thompson and Nohinohi had been smoking synthetic cannabis before the crash.

The Porteous and Keene family members joined Christchurch mother Karen Dow at a meeting with National leader Simon Bridges and his MPs to push for the Government to take swifter action on its plan to tackle drugged drivers.
Dow’s 23-year-old son Matthew was killed in a crash with a woman who had been drinking and taking drugs before she got behind the wheel near Nelson on New Year’s Eve 2017.
Dow presented a petition calling for random roadside saliva testing to Nelson MP Nick Smith last week but the petition has been reopened for a week to seek more signatures.
The Government has prepared a discussion document but it has not yet been released for public consultation despite Deputy Prime Minister Winston Peters telling Parliament last week it had been signed off by Cabinet last September.
National claims the Government sat on proposals from police and transport officials for 17 months.

I can’t work out why the Government is taking so long to move on this issue. A discussion document is merely the first step in the process, and if it was prepared last September, why on Earth is it not out?