PJ, emotion and bias can contribute to a reluctance to comment, similarly there may be problems with highly respected / experienced crews, or due to cockpit gradient.
However, before these problems are encountered, the PM must have formed an understanding of the situation. This understanding would trigger an assessment (decision) to intervene or not, and if so, how.
The significant problems of intervention appear to be at this stage of the monitoring process; either the situation is misunderstood and it is concluded that intervention is not required, or with understanding, the need to intervene is withheld due to other reasons including emotion/personality/cultural issues.
My interest is with any weaknesses in situation assessment and experience as it is these which could affect both PF and PM.
In the worst case the PM may not understand the developing situation, neither the PF; in this instance the concept of independent dual assessment (cross monitoring) fails.
A more likely circumstance is that both PM and PF have a partial understanding, which with added complexity of time pressure and low experience level, results in a late and weak intervention.
Furthermore, the increased workload demand in modern operations, particularly on the PM, reduces the opportunity to monitor.
A further aspect is that monitoring skills may be poorly taught or understood.
In many discussions, e.g. AMS, awareness is often overlooked, instead favouring the more emotive personality/cultural aspects. However, if this type of accident is reviewed avoiding hindsight bias, situation awareness, experience, and timing are often dominant contributors. Also, they are issues which evolve relatively early in the chain of events, e.g. AMS approach vectoring, high / fast, late GS capture.