Mainly, as btrdux points out it’s destined to fail if these crew have to layover in HKG. Omicron is rampant outside of HK (albeit largely harmless in healthy vaccinated people), and crews will contract it, triggering huge numbers of close contact PB incarcerations upon arriving and testing in HK.
To make it work requires “slipping” crew nearby, limiting time in HKG to transits only, and layovers in less monomaniacal locations like BKK, where crews are not tested systematically on arrival.