Because at "equilibrium" there is no net movement. Our cells use differences of solute, differences of electric charge to pump things across the cellular membrane. Our cells need food.. It pumps glucose (First thing you need to make energy) through the cellular membrane by using the net difference of glucose concentration. In other words, the extracellular matrix has more glucose concentration than our cells so to try to REACH equilibrium, glucose gets pumped into our cells. Then our cells use it (or store it if we have excess) to make ATP. Our cells need to be able to move things around (macromolecules, waste, protons, electrons, etc) for it to work properly, and at equilibrium there is no net movement.. leading to apoptosis (cell death)
