It's really a lack of training mostly at the sub contracted out gates and the insanely complicated process with a few hundred keystrokes involved that even a trained and experienced gate agent has to go through to get it done. When the lonely barely trained outstation agent has a million other things to do the jumpseater becomes a low priority.
I had to call DL customer service once because the outstation couldn't figure it out. They were able to list me and print a jumpseat request pass, then the local agent was able to clear me. The system sucks and is certainly not 100% reliable, show up early.