Then why does Galactus keep getting his ass kicked again and again and again by character with a tenth of the power as Dr. Manhattan? He has to be the dumbest villain ever to be able to eat entire planets yet keep getting punked by puny superheros, Fantastic Four, Thor, Hulk, Dr. Strange, The Beyonder. Dr. Manhattan has mastered science, the only thing Galactus has mastered is eating and falling down for much smaller opponents. He is the King Kong Bundy of the Marvel Universe. Dr. Manhattan could easily beat him and then rest his glowing blue balls on Galactus' forehead. Only Marvel fan boys that get ass sore at the idea of a non-marvel character beating their biggest jobber would think otherwise.
Because of plot and contrivance.