A lot of this comes down to economic change: what local economic activity exists in remote areas is much less labor-intensive than it used to be, which means that the Labor base in those places no longer exists, the workers having been replaced by machines. Particularly in Western Australia, much of what work still exists is now performed by workers who live in the capital and fly out in shifts, and those workers vote in Perth rather than in their places of employment. Non-metropolitan malapportionment (which has finally now been abolished all across Australia) also tended to magnify the remote Labor vote by giving small outlying towns their own underpopulated constituencies: consider, for instance, the seat of Kalgoorlie in Western Australia, which was safe Labor for as long as it was based around the town of Kalgoorlie but fell to the Liberals when electoral reform led to its being significantly expanded.
Note that I have referred here to remote seats rather than to rural seats. In what we would think of as rural areas (that is to say, settled areas without large population centers), Labor has never done well, as one would expect. Consider the electorate of Gippsland, which was created at Federation and in the 120 years since has never returned a Labor MP.
Awww I just learned Kalgoorlie no longer exists. It was awesome for its massive size.
Durack is huge too of course but not THAT big. Kalgoorlie was like the size of Western Europe minus Scandinavia.
