Frequency is less important than profitability. SQ, CX, EK, QR and a few others manage to operate a Perth route internationally because of their onward connections but QF can't.
Unfortunately Sydney is located in the wrong part of Australia for connectivity with flights from most other cities going in the opposite direction. If Sydney was located around Broome it would be a reasonable connection from other cities for travel into Asia or on to Europe on QF, however being where it is it's too much of a detour when the competition are going more or less in the right direction. PER - SYD - LAX yes, PER - SYD - LHR no way.
QF seem to have followed the wartime strategy of the "Brisbane Line" and abandoned the rest of the country to foreign airlines.