I've only been there since the disaster but having seen film footage of the stadium at the time, the signage for the outer pens was almost invisible. The obvious place to go was the central pens, particularly when it was clear that thr game had already started. But the operational plan was supposed to deal with that, by sealing off those pens if they were seen to be full, and directing fans to the outer pens.
It should have been clear well before kick-off that the central pens were already dangerously full. In fact, it WAS clear, as TV and CCTV footage later showed. Yet again, the Match Commander, Duckenfield, failed to notice or react. Once the gate was opened, the disaster unfolded as an unrestricted flow of fans instinctively headed into the already overcrowded central pens, which shouldn't have been allowed to happen. The final piece in the jigsaw was the collapse of one of the crush barriers, which led the crowd to fall forward, crush people under foot and suffocate those packs so tightly that they simply couldn't breathe.