I'll give a possible explanation from the "other side"

The common perception in Australia, is that to get to the USA, the (only) way to go is via LAX.

I remember 12 years ago when I took my first trip, I was surprised that UA flew to SFO.

Even on my last trip back home, my family couldn't get their heads around the idea that I had flown via SFO - constantly mentioning my return trip (how long will you stop over in Los Angeles???).

I'm not sure how many UA fliers are OZ-US-OZ rather than the vice versa, but that's a possible reason....