@nh @pervognsen @dneto @zeux
Because down is a far more common action than left. Why move a finger for the majority of your navigation?
Besides, vim has much more effective navigation keys within a line: w,e,f for moving to next word, end of next word, or next matching character.
Down doesn't have nearly as many keys (mostly / to search).
I think people greatly overemphasize the importance of hjkl.