Stacks of particulate stuff like sand and grain tend to act a like a fluid when stacked or piled in containers like a silo. You don't feel the pressure in the deep bottom of a pool only from the top, you feel it from every direction as pressure. The mass of grain in a silo pushes against the sides almost as much as down. Think about what would happen to the grain if the silo were magically removed in an instant. It would spread out into a larger diameter pile. This is how we can store things in a silo without absolutely crushing the stuff at the bottom into dust. The science and math behind why it happens is complicated and beyond my ability to better explain this early in the morning, but I'd guess that balloons in a silo would behave similarly. The pressure on the ballons experiencing the most forces would be coming from all sides, like the pressure differential you feel when diving in deep water. That pressure would tend to decrease the volume of the ballons, possibly making them less likely to pop. At a certain point you'd just have big celled foam made of latex rubber and you'd be crushing that.