Because there are about 10 times as many people in the world that use A4 instead of US Letter: https://en.wikipedia.org/wiki/Paper_size#/media/File:Prevalent_d

Because there are about 10 times as many people in the world that use A4 instead of US Letter: https://en.wikipedia.org/wiki/Paper_size#/media/File:Prevalent_default_paper_size.svg https://en.wikipedia.org/wiki/Paper_size#/media/File:Prevale...