Two reasons 'planes are full' on QF include that many through corporates/government departments and agencies are wedded to QFd, and to a lesser extent QFi, because domestically, alternative carriers lack the route network of QFd.
Secondly, as discussed elsewhere, on some routes such as London, QFi has over the years dramatically reduced seating capacity. Yet Australia's population has soared compared to 30 years ago.
If you took a decade or 15 year view the 'profits' story isn't nearly as good. If businesses like QF delay capital expendture on expensive new aircraft, that can make 'profit' higher, but it can be (long term) a mirage if the clunky old aircraft begin to have a cost per seat km disadvantage compared to other airlines.
