Sad news. AW139 is a very capable aircraft even in the most adverse conditions when used to its full potential. The UK SAR crews have to routinely explore poor weather conditions with low level IMC ops day & night.
Senseless loss.
Yes times 3.
But the fact is (how insensitive the timing is for making any conclusions), SAR and military crews are trained for it, and train for it in their flying program.
The crew flying the VIP 139 is not (up to it), no matter their former experience.
And you brake the rules if you take off VFR in fog (or into fog patches).
All my sympathy goes so far to the crew and pax.