but their ethnic culture was so dominate that both shut up about what they clearly saw the way things were going (badly) rather than cause loss of face of the PF.
You are entitled to your opinion & cultural biases.
But the NTSB accident report does not support such conclusion. In fact earlier in the approach (around 1000' AGL) the Observer pilot noticed the high sink rate and he spoke up. Six seconds later, when the high sink rate remained, he spoke up again.
So clearly he wasn't concerned about "loss of face" of the PF. He did not shut up.
But none of the pilots noticed that the airspeed gradually deteriorated from 137 kts MCP target speed down to 120 kts. And this loss of airspeed was only detected because at 200' the automated callout made the PM check the airspeed.
And because the pilots assumed that A/T will take care of the airspeed, none of them noticed when the airspeed continued to decay to 109 kts. Like before, PM only checked the airspeed again when the 100' automated callout was made. Go around was initiated 1/2 second later but it was too late.
Again Asiana demonstrates that while pilots may notice "obvious" events such as high sink rate, they have difficulty perceiving more gradual deterioration in state (i.e., the speed decay). They were already 17 kts below target speed before the PM noticed it, and only because an automated callout prompted him to look.