Overseen by Steve Perrin, original system-wrangler for RuneQuest and thus the father of Basic Roleplaying, the Superworld game line was an outgrowth of and elaboration on the Superworld booklet from the Worlds of Wonder boxed set. Worlds of Wonder was an early attempt to push the idea of Basic Roleplaying as a generic RPG, since it presented the original Basic Roleplaying booklet with some rather perfunctory genre booklets – Future World, Superworld, and Magic World.
The cynic in me suspects that the actual motivation behind Worlds of Wonder was to find something to do with an overstock of the Basic Roleplaying booklet – with second editions of Call of Cthulhu and Stormbringer rapidly taking the step of integrating those rules into their main text, which was found to be preferable to having to flip back and forth between the Basic Roleplaying booklet and the main book for the game in question, I think Chaosium probably found themselves having to work out what to do with the excess booklets they’d printed.
That theory would certainly explain the total lack of support that the core Worlds of Wonder box received, and the swift abandonment of most of the tangents proposed therein. Future World was dropped completely; Magic World was abandoned and though a game of that name was eventually released in subsequent years, in practice that version didn’t have all that much to do with the original Magic World booklet beyond the title; it was more of an attempt to reprint the late-edition Stormbringer rules in a setting-neutral fashion after Michael Moorcock pulled the Eternal Champion licence.