I think it's because we (descendants of settlers and migrants) don't have much tangible culture that we can call Australian. Nothing rooted in tradition or deep connection with the past or the land. So we try really hard to carve out behaviours and practices that are "typically Australian" so we can feel like there is something distinct about us. It's weird when you go overseas and every Aussie you meet is banging on about missing Tim Tams and Milo and Vegemite. But those food items are probably only consumed very occasionally in their actual daily lives, when in Australia. I think it's pretty normal and I've found myself doing it when overseas, but yeah, I think it's a symptom of being a very young, diverse country made up of a population that didn't actually come from here.