Superman's creators Siegel and Shuster were teenage, science-loving, first-generation nerds, and for all Supermans power, an intellectual discipline governed his early stories. There was a quasi-Darwinian explanations for his strengthmillions of years of evolution, and, later, the heavier gravity of Krypton. He may have seemed to fly in the cartoons, but the early comics assured us he was really just leaping like a grasshopper. His earliest foes were spies and run-of-the-mill crooksreal-world concerns that justified the escapism. Captain Marvel could fly for real. His creators, adults with less need to prove themselves serious thinkers, regarded themselves as purer childrens entertainers, and his stories read as if an excited child was telling them to you:
And whenever Billy says SHAZAM he gets the power of six old guys whose names all begin with S, H, A, Z, A an MSolomons smarts and Hercules strength and Achilles heel, I mean courage, and Zeus and Atlas and Mercury, but then he can never say SHAZAM unless he wants to turn into Billy, which is a problem because his wizard ghost friend who gave him the power is named Shazam tooAnd his best friend is a talking tiger and Shazams house can take Captain Marvel anywhere in any dimension and his biggest enemies are this short, bald, ugly mad scientist who has all these evil inventions, and this worm with a radio loudspeaker around his neck, and theres his sister Mary Marvel and the Lieutenant Marvels and Captain Marvel Junior and Uncle Marvel
This all plays really well when your target audience is seven, but today's complex comics continuities tend to prefer things that have to be explained.