Well, for starters, it’s the reverse 😆

And you’d probably have to ask a linguist, but I would think it’s gotta be related to ‘Wagga’ being two syllables, and ‘Woy’ being one. Not only is ‘Woy Woy’ short enough to begin with, but ‘Woy’ is also probably more prone to mishearing than ‘Wagga’.

Wagga Wagga means place of many crows. In the aboriginal when you say the word twice, it makes it plural. So if you just say Wagga, you’re saying crow.

We were probably saying it wrong, but in Northern Victoria we just said Wagga once.

Wallan, VIC is actually Wallan Wallan - lots of wind. But is officially shortened to just Wallan. Others I know of are Bong Bong and Gumli Gumli, NSW. Billa Billa, QLD.