probably because defenses have a general idea on what the play will be if it is indeed a run play.
actually...adrian peterson can really pound it in and run guys over and consistently run off big plays...pair him up with dayne so neither will be exposed to injury and you really have a killer duo. if peterson is available...go for him.
but i really do like the idea of 2 big backs alternating and pounding the defense 50+ times per game. would really wear down defenses and open the passing game through play action. would limit david carr's throws and would thus limit the mistakes he would make. hunt is no slouch and can pound it in and can run off a big play every now and then. use dayne in short yardage situations and use hunt as the relative "change of pace" back, even though its not a big change, the idea is to have 2 big bruisers. could defenses really keep up with bringing down 2 backs who weigh an average 240lbs?