Sorry for dragging up the EK PIK debate but I am sure the reason that NCL was preferred, was based on the worst case scenario of where to go if you can't get back into GLA later due to weather and you remain stuck where you divert to. There is no question that NCL is far more suitable than PIK in such a situation and for numerous reasons, many of which have been mentioned already.
Historical weather also points to the weather at NCL being considerably better (CAVOK) at the time the diversion took place.