Originally Posted by
seibaatgung
why is a front dynamo hub more efficient?
There's nothing inherent in the dynamo being in front that makes it more efficient. It's just that the makers of high-efficiency dynamo hubs have decided to made them as front hubs.
There's also a packaging problem: there's just more going on in a rear hub than a front hub, so adding the dynamo works to that makes it more complicated.