I agree that a certain aptitude or predisposition could be responsible for it.

There is another aspect which I will add: the ‘softest’ parts of the liberal arts curriculum — International Relations would fit here — was until recently reserved for aristocrats. The children of farmers and factory workers would ostensibly have no use in learning The Great Game. The best players of the game are those who need no employment.

Those of us from anything but the uppermost classes back then would be stumbling into the edges of a world they can dimly perceive, to serve as clerks at best.