Not all activity is economic activity and not all economic activity is valuable. People outside the US aren't generally expected to work 24/7

It's totally incorrect to state that the area served by either Sydney or Melbourne airport has less economic activity than the area served by "any airport in the US", or even the vast majority of US airports, so whatever laptops-at-airport (and I suppose airpods-in-ears) is a proxy for it sure isn't economic activity.