You seem to think that because it's possible it should be accommodated, regardless of the risk.
No, what I think is there are many tools in your arsenal to deal with risk. If this particular aircraft entering your airspace has saturated it to the point where you can accept no more, than fair enough. Was that the case on this day? I doubt it. Australia slaps itself on the back incessantly about how good it is. I doubt that too. Australia thinks it is the world leading ANSP, that's bull****. There is serious cultural change that needs to take place in there.
Sorry, that's not the way it works.
I've a pretty fair idea how it works.
Sure there are options but unless you're there on the day and have the whole picture how can you say which if any were available?
Was the aircraft offered transit at a lower level? Was the aircraft offered transit OCTA?