First of all I will address the issue of the Melbourne service. This service was removed because of low loads when it was a part of a shuttle from Sydney or because of the bad utilisation of the aircraft, as mentioned by Wiggy, when it was a terminating flight direct from Singapore. Cabin crew costs pale into insugnificance compared to the costs of having an aircraft sit on the ground or fly with low loads. At certain times of the year the loads were ok but BA being a schedualled carrier has to fly and operate a year long schedual and unless a flight is full it cannot make a profit it has nothing to do with the crew costs.
Not true that a flight
cannot make a profit unless it is full. I pick that up because the issue of posters making things up was raised. I'd hazard a guess that full flights don't always make a profit either. It's a lot more complex than that.