From somethign I've been told (many years ago / unverified source, etc..) is that "mail" usually is a filler for planes & such. and AUS is a long way away.. so, with Covid: few flights to Oz.. Few ships directly to Oz.. Big fancy paid stuff get priority, US mail (or any mail that is passing thru the US: Canadian mail for instance) is 2nd class, and fills up whatever hole is available, on whatever available flight / boat..
Very true. Mail isn't sent on a Mail Plane any more, prolly not since Moses played second base for Jerusalem. Mail is a 'filler' on passenger flights and no passenger flights = no mail. I just wish big companies (Australia Post/USPS) would stop blaming each other and just be honest with their customers.