To be honest I think the “sarcy, judgemental” responses are more to do with your attitude that this country owes you something than your question itself. Yes the UK allows you to transfer pension overseas which is a good thing but it is one of the more advanced in this area. Australia does not allow it and never has. However given the amount of people coming and going in Oz in recent decades I can see this changing in the future.
You can’t expect immigration to just take your word for it that you’re leaving permanently. The fact is, when you have permanent residency you can return to the country at any time. If a temporary resident wants to leave the country then they’re happy to give them a refund as they couldn’t care less if they blow it all, they’re not going to be retiring in Australia, therefore it’s none of the Australian governments concern.
If you though took a refund and went back to the UK and spent it all, you could still go back to retire in Australia and live off state benefits. I’m not saying this is your intention at all but it may be for some people and that is what they are looking to avoid.