There are numerous factors that affect travel prices around the world; however, Australia has the "perfect storm" of factors that contribute to high airfares.
A flight's price is inversely correlated with its length. A ticket increases dramatically with each stop. The viability of discounts and the type of plane used are influenced by the volume of customers, which has an impact on profitability. On the busiest routes, there is the most intense competition. Finally, there is a direct correlation between pricing and airline quality.
As a result, it will be expensive to travel in Australia on a reputable airline over a long distance on a route with limited traffic and little competition.