It is interesting that it was made in the 1980's. It's only real competitors would be the Superman spin-offs and then Batman in 1989. I feel like the Wonder Man movie must have not been a big hit but maybe became a cult classic afterwords. Perhaps the rise of real Superheros is what sparked the interest in that big time director wanting to make a movie about it.
It might be that the MCU is like Toy Story's world. In real life, Star Wars and Jurassic Park are the only movies that launched major action figure lines.
Superman does exist (as a fictional character) in the original Spider-Man movie.

