Why don't forest fires in Western Australia get as much attention as forest fires in the southeast of the country (including SA)?
Forest fires, and natural disasters in general, get attention when they affect people.

Bush fires outside of metropolitan Perth or far away from populated areas do not affect many people. Therefore, media attention is diverted elsewhere. This is not unique to WA: you have the same in NT, northern SA, and the west of eastern states.

This is also not unique to bush fires. Volcanoes only get media attention when they affect people: recent examples are Fuego in Guatemala or Kilauea in Hawaii. The other 50 or so active volcanoes in 2018 get close to zero media attention, because they do not affect anyone (or at least, they do not affect people that the Western media cares about).