It looks like Larson had trouble figuring out the composition of this comic.
I’m guessing it went like this: He needed to put the sign somewhere that it could be read, so he put it up high. Then he put the door high so that the panel wouldn’t have a lot of empty space. But then, he needed to add stairs to the door, and suddenly there wasn’t enough room for all of the victims. So, they’re hanging in this strange little space next to the stairs that probably wouldn’t exist in real architecture.
Suspiciously similar to a trick parents use on their children. “Do you want to eat the peas first or the carrots first?” Gives them the illusion that they made a choice about what to eat.