The early 80's kicked off a wonderful era for Marvel Comics; one where they were so desperate to get their properties made into films that they greenlit insanity like this or the Roger Corman Fantastic Four movie.
Apparently the success of the Chris Reeve Superman films set off a bit of a panic at Marvel, and the result was a clusterfuck of insane movie deals that they're still digging their way out of.
Like the various scripts developed during the 80s for New World Pictures, which produced Dolph Lundgren-starring "Punisher" movie and, thanks to New World's collapse, an unproduced Punisher II that supposedly would have hewed closer to the comic, and two unproduced scripts for a "Wolverine" film and a "Wolverine and the X-Men" sequel.
As well as half a dozen other loopy movie/TV ideas Stan Lee thought up before leaving New World, like an Ant-Man series (and not about the one from the Avengers) and a "Dazzler" tv-series.
Not that Marvel wasn't desperate for a lot of stuff in the 80's, but Marvel's desperation had nothing to do with the FF movie by Corman. That was made so whatever company had the rights could keep them. Most movie licenses require a movie be made with in X number of days before they revert back to the copyright holder.
It's why the Corman film was never officially released. The contract didn't require it to be, they just had to make some kind of movie.