One problem is that the park wishes to move ALL registration to reservation.gov which does not allow reservations within 72 hours of your visit. I'm local and 3/4's of my stays there involve finding out at the last minute that I'm free for a couple of days from work. Currently, I can go and self-register for any of the non-reserved sites at any of the 15 kiosks. If reservations are moved to reservations.gov, those trips would no longer be possible as I could not get a reservation before my time off from work was over.
It may seem small to those living far enough away to need to plan for time to visit there, but for the locals (many of whom moved here to have such access) last minute trips to the park are a mainstay.