1. Vast Distance and Complex Logistics

Distance: There are over 7000 kilometers (4,300+ miles) of ocean separating China and Australia, making the geographical span enormous. Executing a large-scale beach landing invasion over such a vast distance would be tremendously tricky. Remember the largest sea invasion in modern history, D-Day, was only possible because of the short distance to travel overnight with no military spy satellites to see the allies invasion force on their way.

Logistics: An invasion would necessitate a massive logistical endeavor, including transporting troops provisions, and gear across the sea and this would overextend China's supply chains and encounter major hurdles like Australia's innate geographical seclusion, rendering a prolonged military offensive unsustainable, again learning from history it was the supply chain that stopped Erwin Rommel's advance across North Africa during WWII and that was a Sunday outing when compared to the Australian desert.

2. Australia's Strategic Defence Partnerships

Alliances: Australia is a key ally of the United States via the ANZUS accord (while ANZUS is commonly recognised to have split in 1984, the Australia–US alliance remains in full force) and takes part in defense collaborations with other Western leaders like the United Kingdom and regional mates like Japan. A Chinese attack on Australia would likely prompt a collective defense reaction from these formidable allies, notably the US which retains substantial military assets positioned in the Indio-Pacific zone.

US Military Attendance: The US wields considerable air and naval strengths in the Indio-Pacific, and the US military's aptitude to project dominance in the region would function as a hindrance to any outright military aggression against Australia, not to mention the US bases in Australia

3. Australia's Defense Capabilities

Australia's military might not be as big as China's, but they've got some pretty advanced stuff going on, especially the tech and equipment. Their navy, air force, sub fleet - all top notch and would give any invader a heck of a fight.

And then there's the fact that Australia's just so dang big and empty. Lots of harsh desert and wilderness to get lost in. Occupying the place wouldnt exactly be a walk in the park, which is one major reason Japan were unable to invade during WWII.

There's also the money side of things. China and Australia do a lot of business together - China's Down Under's biggest trading buddy. A full-on invasion? Thatd muck up those sweet economic ties but good, not to mention getting China the stink-eye from the global community. China's economy is tied up with everyone else's, so they'd be playing with fire on that front and if things went hot between these two big trading nations the world economy would take a massive hit too. That alone makes this a no-go.

Lets not forget how the rest of the world would react either. The UN and other big players would lose it over China invading Australia. Huge diplomatic mess, sanctions, the works.

It could also spiral into a much wider war, dragging other countries in. No one wants a global war on their hands over this. The risk is just too dang high.

China's got enough strategic stuff on its plate. This Australia business would be one distraction they just don't need.