eric, I appreciate the sentiment (I too find the choice to bury them unfortunate) but I am pretty sure that Oz isn't looking to the UK as their primary ally/support if and when China comes knocking, all AUKUS considered.
Based on some of the nuttier logistics and systems decisions that over the years have happened over here in the land of Yanks, I am going to guess that someone ran a spread sheet / calculation on what it would cost to box them up and ship them to Ukraine from OZ, along with spares and tools, etc.
It was discovered that it would cost more money than they wanted to part with.
(And maybe someone knew someone who could bury them at a certain price and a deal was in the works?)
Getting someone else to cover the shipping may not have occurred to the functionary who was looking into this...
There's a supply/logistics nuttery thread in MIl Aviation with similar stores of "Wait, you did what?" as regards that side of mil aviation. This seems to fit in a similar category.