Apart from what aircraft do QF have to fit the route, while they have a base at PER domestic, i wonder if they have other fixed costs operating out of PER Int as well (gate costs etc, having staff over there or whether they can rotate J* staff or boarding and check in and other things they may need over there??) If so it probably made a lot more economic sense when you had multiple flights a day to HKG, SIN, NRT etc... As every flight was cut the costs were probably spread over fewer flights, the scale and the critical mass dropped probably along with QF front of mind awareness of local Perth people so in the end one flight a day out of the Int terminal might be uneconomic, multiple flights daily on competitive products with a bit more determination to succeed and market the services out of Perth might have been viable...