Maybe because those of us who like turkey seem to really like it, buying a whole turkey doesn't seem odd. I could happily eat turkey sandwiches 3 times a day for a week (and the turkey would be long gone before then).
Now there's a real fan for you!
It is unusual to see turkey in parts here.
I'm pretty sure that it hasn't been a big, established feature of Oz cooking. That could explain it.
There is not nearly
as much available .... apart from at Christmas, but even then, nowhere near as much turkey as chicken.
But then, unlike in the US (I gather from previous discussions here) we tend to have more smaller portions of bigger items of food available for sale here .... like pumpkin, for example. I would very rarely, if ever, buy a whole large pumpkin. But I guess folk with big families would.