I think this is also due to the fact that an air spring hardens when more weight is put on the wheel and then no longer offers the properties as intended. A steel spring adds a lot of weight and titanium springs are expensive as hell. If the luggage is carried along on the dip tubes, this increases the unsprung mass and then also takes away sensitivity. A suspension fork is then again just ballast and more susceptible to defects than a rigid fork. Perhaps that is the consideration for many.Thanks for your reply and tips about travelling there especially the wind direction, I am surprised more expedition bikes don't have front suspension, I have not seen another Roughstuff that has it and Surly dropped it from the Troll sometime ago.
I have ridden all my tours with suspension (at least at the front), but I never had much weight on the fork or handlebars.