Men don't see it coming because they don't care. Quite frequently men are in bad relationships that don't affect them much but they generally don't walk away.

Women pull the trigger when they can't take it anymore.

This could be the reasoning of someone with survival bias though.

Unfortunately, life can be complicated, e.g. family member went through undiagnosed schizophrenia for many years, one can imagine how that upset the marriage assumptions prior to the mental health issues.

I was talking more about the average situation.

I would assume serious mental health issues are the edge case in this scenario.