With pressure, you have more stuff in one area of a container and less stuff in another area of that container. The space:stuff ratio in the more compact region is lower than the less compacted area. Space is a vacuum (suction cups wouldn’t work if it wasn’t), so there is a force that pulls on the compact matter. This force is from the center mass of the compact matter and all directions out of the center. This matter would experience this force until the container has an even distribution of the matter.
I just claimed that vacuum is pressure. What is gravity but a vacuum too?
Space as antigravity, lol.