If two similar accidents occur in the same area this is essentially meaningless unless we can determine a precise common cause, anything else is just random chance.
Common themes have been alluded to:
there are commercial pressures to "trim" towards the basic regulations rather than build the "gold plated" standard
a culture of not bothering too much
OEM briefings identified that torque settings were higher in the North Sea than in other areas of the world, so stress loads were higher