And the new regulation will make it harder for the Park Service to catch poachers. As I understand it, one of the main reasons for the original regulation, which requires firearms to be unloaded and inaccessible (e.g. in the trunk of the car) was to help prevent poaching within National Parks, where it's easy, as many animals have lost their fear of humans.
Just how does it make it harder to catch poachers? If someone is going to illegally poach animals, they are going to disregard the law about not carrying guns into the park in the first place. It is still not legal to discharge weapons in a national park without due reason. Any gunshots will still attract the same amount of attention.