The frog cube is the Genjutsu, that's like Itachi not knowing he has someone in Tsukiyomi, the cube world is the genjutsu, and yet again, for all we know the pains could have been on the way as soon as the genjutsu was used, Jiraiya had a small talk, and then killed pains bodies, it seriously makes no since for what you just said.i said its possible that they were immobilized cos if not they could have come, but they only came after jiraya released it and genjutsu could have still disrupted them they don't have to to somehow teleport in the cube somehow to show that actually works, the paths chakra flow was disturbed and none came to help that might show that they too were immobilized, it doesn't make sense for them all to randomly appear in the cube dude. It might be that they were not in genjutsu or they were but that is up to us to believe.