Hardly a mystery, unless you live under a rock or are a flat-earther or something
They are to satisfy ADR requirements wrt wheel coverage (as you well know).
Also found on many imports, until discerning owners rip the ugly things off
Why they would be required on an AU Falcon/Fairmont/Fairlane etc (solely designed for the domestic market) makes you wonder if the designers had ever consulted the local regulations
AU's
.