You may be unaware that the exemption given to aircrew by the Federal Government comes with many restrictions that significantly reduce the chances of crew acquiring the virus whilst away. If crew do not comply with those restrictions/procedures, then they are required to be isolated upon their return.
My experience was that I had to inform my managers ( major Aus Airline) as new requirements came out regarding crew exemptions and they were implemented late and poorly. The many restrictions you speak of were not communicated to crew through email, text, in tam, or face to face without significant lag and prompting. As for the last sentence......nobody checked, nobody communicated the requirement. It was poorly managed at my Airline. Zero leadership displayed until about 24th March.