Flagship route or not, it’s an aircraft, it breaks down. Engineering isn’t available instantaneously either like it used to be, especially on the other side of the world at an airport with two departures a day. A spare part might need to be shipped over from the US. Engineering departments are still struggling to maintain some form of basic inventory. Getting a part from Seattle from what I have seen at my employer recently had been nothing but a nightmare, plan 1-2 months.
Seat availability is very tight at the moment especially on the Kangaroo route. I know people last week who had to route London to Sydney via San Francisco due to lack of availability.