Why do the Boers, of all people, love rugby, of all sports? Other than cricket (arguably), it is quite the least likely game for such implacable foes of the British ruling class of yesteryear. Still, the Tories managed to love the Boers and their revenge republic, which was just as improbable.
For that matter, why do the Welsh of the Old Labour persuasion so love the game of those who gave them their martyrs at Tonypandy? I understand that rugby was, and to an extent still is, a way of expressing a Basque or Catalan identity in south-western France, distinct from the football-loving French.
In Argentina and Chile, it is a way of expressing longstanding ties with Britain (there were far more British subjects living in Argentina than on the Falkland Islands at the time of the Falklands War, for example), and in Portugal of expressing very longstanding ties with England specifically, although it is a small minority pursuit in those countries. In Australia and New Zealand, the link is obvious. In Italy, I just don't know, although I'd be fascinated to find out.
But in South Africa, in Wales, in the Scottish Borders - isn't it just a bit English, and posh English at that, for them? So what's the story?
But then, look at the cricket-playing (and the Episcopalianism) in the Scottish North East, in no sense an Anglicised area, but rather one where the SNP does well electorally. For that matter, look at the popularity (real or otherwise) of football among the English middle classes since 1990, even though England has not won an international football tournament since 1966 (at home), when football was pretty much a working-class peculiarity.
There's a book in here somewhere.