IIRC, the original type-writer layout was much more efficient. So efficient that typists typed so quickly they jammed the machines, because the next hammer would strike before the last one had returned to its position. The QWERTY layout was designed to slow them down. So as more companies adopted QWERTY typewriters, more typists learned to type on them to increase their attractiveness as employees. This steam rolled and more companies started producing QWERTY keyboards because more typists could type on them. It then became the standard because that's how everyone learned to type.

I remember reading about this in a class I took last year but I can't find the article. I'm pretty sure this is correct as far as broad strokes are concerned, but maybe someone can find a source or fill in the details.