Perhaps they are then protected from feral deer, you know those lovable bambis, that nearly ate (destroyed) NZ's native forests, (when there's nothing else left, ring bark the mature trees) and now threaten the same here!
Or perhaps it's feral pigs, goats, camels, dogs, hares, rabbits and donkeys!?
Or perhaps just feral weeds, like the runaway rubber plant vine!?
Covers whole forests for up to 2-3 years, then like all biennials, dies off, leaving nothing but a huge dead and bone dry fire hazard.
While it's hard to fathom the minds of vote seeking pollies, it's far harder to fathom the minds of those who advise them.
Until you see a Czechoslovakian film; titled insane, which depicts a scene, where the inmates have taken over and run the asylum!?
Rhrosty.

More fundamentally, one might also ask: Why protect National Parks at all? This is not a silly question.

Some national parks were proclaimed because they were places of special beauty or environmental value. I can see a good case for protecting such land. During the 1970s and 1980s, however, many left-leaning State Governments converted a lot of vacant crown land or state forest into national parks in order to gain the greenie vote. Did such lands deserve protection? Generally not.

By the mid 20th century most vacant crown land owed its status to the fact that it was infertile and unsuited for agriculture. This logically lowered its need for protection so that there was no special need to protect it from needs such as mining. Declaring so much vacant crown land as national park was a mistake!

I agree with the author, governments of all stripes have much to answer for there.
As to "protect from what?", I'd say the greatest need is to protect our NP's from the government itself!
Oz is a harsh land and the public service, overseen by corrupt and inept politicians answering to a feckless and ignorant electorate, is the worst possible "gardener" to deal with the harsh regimes necessary to successfully maintain it.
More input from Indigenous Aussies and greater community involvement would be a good first step to resolving this, IMO.