It's simply not the busiest time of year of the LAX route .. For bums on seats ... And especially not for revenue.
Majority of QFs pax during the year on the LAX rites are people travelling on business. They want flexibility and/or premium seats = higher fares = more revenue. These business travellers don't travel on the 'business shut down period' over Christmas .. In either direction.. So of course QF are gonna flog as many seats at whatever price just to fill the planes over this 'low bums on seat and low revenue period'.
. Trust me I have done enough Christmas trips to LAX to know the difference in the type of pax and the number of bums on seats as compared to the rest of the year