"A 4-engine plane can safely fly with one shut down, however, when you have dozens of airports around you, drop an engine and decide to still head out over thousands of miles of cold ocean, I fail to understand why the Capt did not choose to turn around."
You miss the point. A 4 engine airplane can often safely fly with TWO engines shut down. Thus loss of 1 is an issue to manage, and it might be prudently managed by pressing on -- IAW with 70 years of industry experience.