Just some guesses: grades, lack of CTC, lack of sidings, restricted clearances, track ratings, to name a few that come to mind based on previous discussion of the idea. Via CORP would mean no double stacks, no autoracks, no long cars, no really heavy cars (is CORP up to 286K everywhere?), short trains to fit the few sidings that exist. IOW, UP might send select emergency trains that way, but nothing serious. Besides, is CORP actually operating anything over the hill yet, or is the route south of Medford still embargoed?