For big traps you need lots of hormones.
I haven't seen a single clean powerlifter with any trap development to speak of, and I know some who have killed themselves with deadlifts for decades. Some other muscle groups seem to grow a little without drugs but traps are a really hormone dependent muscle group.
As far as training, tension is king for growth, range of motion and all the other parameters are secondary, as LATS alluded to. Deads usually place the most tension on the traps.