I don't see why there would be so many mofos down there. As Ace's example is right now showing us, they execute those people after holding them for a while. So, theoretically there should only be people there who are in the death row, who are being tortured for information and who are there temporarily for random reasons like our fishman shichibukai, who refused to participate in the grand war. It's logical even Crocodile was there only waiting for an intimate meeting with the axe.