That's a good consideration too, but I think he's chiefly talking about unhappy people, who believe that if they could only move to Elbonia where everything is

That's a good consideration too, but I think he's chiefly talking about unhappy people, who believe that if they could only move to Elbonia where everything is wonderful, they will automatically be happy. Alienation is one aspect to expat depression; another is the realization that other countries aren't magical fairylands that have everything figured out- they are full of ordinary people with ordinary problems, just like anywhere else.