Subdiaphragmatic peritoneum is more absorptive than pelvic peritoneum because the former possess:-

The mesothelium acts as a semipermeable membrane across which fluids and small molecules of various solutes can pass & the peritoneum can absorb fluid effusions from the peritoneal cavity. Water and crystalloids are absorbed directly into the blood capillaries, whereas colloids pass into lymphatics with the aid of phagocytes. The greater absorptive power of the upper abdomen (subphrenic area) is due to its larger surface area and because respiratory movements aid absorption.