Benjamin Schwarz, The Atlantic:

This isn’t to attribute the dearth of charm to some cultural and social declension, although clearly charm—with its emotional, even aesthetic, detachment—could hardly have retained its social sway after that most overwrought of decades, the 1960s. Any culture that celebrates youth necessarily provides stony soil for charm, which is by definition a quality reserved for adults: the young can be charming, which is an inadvertent attribute; they cannot have charm.

Charm as a personal value — that is, a quality that can and should be cultivated, as opposed to an attribute one is born with — is increasingly rarer in today’s society and sadly, that’s not limited to American culture.