Having worked as a dispatcher for BD at Glasgow who at the time handled, AC and AA as well as BD, it was always first choice to divert to a home port. The reasons are logistical and generally the preference of flight deck to operate to an airport they knew. The logistics on the ground are easier, hotels, fuel, ramp costs and taxis all had contracts in place. PIK is used for diverts from GLA in emergency circs and a few weather related but I can see no reason why EK would plan it first divert option for their crews (with the added expense) when it has two home bases nearby. The NCL & MAN flights have came to GLA in the recent past. The flight crew will have spoken to Swissport at MAN & NCL before diverting for handling availability.