It's not unusual to not have many pax on a flight. When I flew to Saudi Arabia for work with BAE systems in the late ninties. There was hardly anybody on the flight from Brisbane to KL, maybe 30 % full. But I stayed on the same aircraft and then flew on to Jeddah. It was 100 % full from KL to Jeddah.
Also a lot of regional services were subsidised by the state governments to give a air link to the west. It makes sense, it takes me on average 43 minutes to fly from Brisbane to Miles on a -8, where as it would take me 5 hours to drive it by vehicle.