[jrochkind1]

I think there are two possible answers.

A) There is a hidden advantage of some sort to the current design that the designers in OP are not aware of or not taking account of. It could just be cost as another poster suggested, or something else.

B) No good reason at all, just tradition. I can't find it now, but there was a post on HN asking why we still used the traditional Western wheelbarrow in our countries, when the Chinese wheelbarrow (what a coincidence!) was so obviously superior. The Chinese wheelbarrow has the wheel in the middle, so the wheel bares the load and the human just needs to push/steer.

[jrochkind1]

Heck, maybe nobody in China ever bothered to improve the shoulder pole, because they didn't need to when they had the superior Chinese wheelbarrow!