In that they lack a gift of understanding that the poorest serf in medieval Christendom enjoyed. Such a serf knew that no matter how mean was his earthly position he had transcendent worth. He had been baptized into it, and when he came to dying he would receive the same sacrament of salvation available to his lord, and his lord's lord. This he knew, and he thanked Christmas for it. In today's common acceptance of a purely material explanation of the universe and all within it, size naturally becomes of utmost importance.
Size can be measured, so greatness is of prime significance for the materialist.
That may be why the taller candidate has in the past invariably been elected President. We may laugh at small comedians, and delight in babies and children but we are inclined to respect tallness of height and thickness of muscle. It has become so in our cosmological considerations. We expect to find greater progress having happened elsewhere than on earth. The time of giants being on earth is past.