The Shazam version was one of the best selling comics of the golden age. When DC sued and caused Fawcett to stop publishing comics altogether (it would be a few decades before they bought him outright), other companies jumped in with their own Captain Marvel's hoping to trick fans of the original into buying it.
MF was notorious for copycat characters, if not in name than visually, like the totally oc donut steel The Bat here. Other villains were Dr. Fate, Plastic Man, Colonel Cold, Tarzac the King of the Sea-I mean sharks, totally not Aquaman I swear. Oh, and their Cap was the last survivor of his home planet if things weren't already stupid enough.