In the wake of the Afghan war, it has become a (bad) habit to get some captives in a container sort of cell. Then you move the container around the world if you want... No heavily armed guards, just a few "contractors" looking after the precious container in a hangar designed just for that, containers!

So big planes (cargo) should be what those "experts" would rely on !

Just a guess... Meaning that small planes are less discreet then big ones and  the "cargo" side of airports is usually not public...!

"What can I do, What can I write, Against the fall of Night". A.E. Housman