Rematch?

Why was there no Rocky Balboa-Apollo Creed III? Creed by all accounts had the second fight won, he refused just to dance out the 15th round, and he still was clearly in astounding shape. Why does Rocky III, then, begin with a montage of Rocky pounding tomato cans? I know they have their private sparring rematch at the end of III, and I know Apollo makes an ill-fated comeback against Ivan Drago, but why did a competitive soul like Creed not clamor for a rematch?