Apples to oranges. SQ or any ME carrier flying from ADL to a hub then onward gives passengers plenty of options for onward connections. QF abandoned sin for dxb as we all know and are flying the remaining widebody airframes to end line destinations.
Singapore/Dubai/KL/etc aren't obviously attractive enough as a end line destination to offer to ADL that would come close with the competition frequency. Maybe if the 738 had the legs it would be deployed.
If it were your business would you throw your hat in the ring with dozens of carriers fighting over the scraps in the most competed for route in the world or would you just stick to monopolies and high yielding routes?