Blame the ambulance-chasing, money-grubbing, get-rich-quick lawyers and the "sue now, ask questions later or not at all" litigious attitude they've helped create for that, as well as the fact that insurance companies will charge you through the nose unless you've done everything you can to eliminate liability on your part and the refusal of far too many people to simply accept that all activities have a certain amount of physical risk; given all that, it's not surprising that UP and other railroads won't allow passenger excursions on lines they've leased.