[wxnx]

The notion of a standard language is a modern idea (not in the sense of modern vs. postmodern, but historically).

The idea that the only valid basis for distinguishing between dialects is geography strikes me as odd, but suppose we accept it as a premise. Why is it less valid to allow correctness to be defined, say, with respect to local borders as opposed to the borders between countries?

[ceilingcorner]

I didn’t say it was geography. American culture is mostly separate from Australian culture. As the US is a unified cultural element, it’s not surprising that a single standard had been established. The downsides of the lack of this are easy to observe: just look at the EU. No single unified language, no unified market, less economic power. Making a Netflix for America requires 1 language, while making a Netflix for the EU requires 29. China isn’t pushing Mandarin everywhere just for chauvinist “cultural superiority” reasons.

It ultimately comes down to politics and economics.