Earlier quoted context omitted.
Because it's fun to have diminutive version of many words. And because it differentiates us from boorish Americans - or as they are also known in Oz, seppos.
I once saw a sign in Australia warning about crossing train tracks. In the land of the free, the sign would have all the coziness of a Secret Service agent: KEEP OFF TRAIN TRACKS - $100 FINE PER VIOLATION But this was Australia. So it actually read something like this: "Cross tracks safely and only at the provided walkways. Or cop a $100 fine. Don't say we didn't warn you, mate!"
Warning
Do not trespass on the Railway
Penalty £1000