The Qantas spokeswoman said cancelling the flight would have been a really poor outcome for customers in Sydney and all efforts were made to get the flight into Wellington.
"The decision to divert was made once airborne, after the boarding and taxiing processes," she said.
Qantas said it regularly accommodates customers in hotels or rebooks them on new flights "regardless of costs" when there's a cancellation, and denied any decisions were made because of financial reasons.
"We understand how frustrating this decision was for our passengers and apologise again," the spokeswoman said.
"Our teams went into great lengths to be able to depart Sydney Airport in time to make the Wellington curfew rather than cancelling the flight, as the severe weather meant there was extremely limited accommodation in Sydney," she said.
"Despite best efforts, once airborne it was confirmed that the flight was going to miss the extended Wellington curfew and had to divert to Christchurch."
She said accommodation and transfers were going to be sourced in Christchurch.
"But based on the times and how long it would have taken to get each passenger accommodation and transport, they would have only an hour or so at a hotel before having to return to the airport," she said.