Here we go...
The minimum RFF category for ETOPS/EDTO is 4.
Learmonth has been assessed as adequate to nominate as an ERA alternate by many airlines.
Most Asian aircrew rely heavily on decisions made by their operations centres in the event of non normal situations. It is common for Asian OCs to place operational convenience ahead of regulatory requirements. I don't think they deliberately ignore the rules, it's more likely a combination of legacy mindset from four and three engine days, and confusing EDTO literature that doesn't translate well from English (there are plenty of confused posters in this thread too...).
It's not a stretch to suggest that they only had Notams and information for the alternates specified on their flight plan and were unaware of the availability of Learmonth.