Gender and economics

From Jacob Levy, re: a Figaro piece on a new economics school in Paris:

« Si on ne fait rien, dans cinq ou dix ans, les seuls chercheurs qui viendront à Paris sont ceux qui auront une petite copine en France », plaisante Thomas Piketty.

"If we do nothing, in five or ten years, the only researchers who will come to Paris will be those who have a girlfriend in France," warned Thomas Picketty.

Apparently no economists have French boyfriends.

The implicit sexism--economists are assumed to be straight men--is probably what Picketty is expressing, but it's not the whole story. For whatever reason, among heterosexual Americans, not to generalize or anything, but different countries are alleged to have attractive men than are alleged to have attractive women. A French girlfriend has more cache than does a French boyfriend. Meanwhile, an Israeli boyfriend probably has a bit more than does an Israeli girlfriend, and same goes for an English boyfriend versus girlfriend. Meanwhile, a Swedish girlfriend elicits oohs and ahhs, whereas a Swedish boyfriend is just a boyfriend who happens to come from Sweden. This is leaving out the classic Asian girlfriend-not-boyfriend and black boyfriend-not-girlfriend biases in America itself.

My question: why? How do some countries and races come to be seen as masculine and some as feminine? Presumably this is what's behind the way things fall.