I heard a political scientist on the radio this last week and he said that publicly, parties on the left of politics say that people should be given the democratic opportunity to "participate in the election process" right up to the last moment. Privately, they don't want it changed as it's historically been the university cities like Wellington and Dunedin where students enroll at the last minute and in South and West Auckland.... which are all fill of seats which generally vote left. Getting rid of Election Day registrations would effect the Greens and Labour party votes more than centre right party votes.