I think there was more to it than that. Before the first Superman movie the idea of a superhero movie was considered childish. Nobody was interested. Superman proved otherwise, but it wasn’t really until Batman 1989 that studios really started to take the idea seriously.I read years ago that the reason Superman never came to the big screen (and same for Spider-Man) was they had to wait for technology to catch up so that making Superman fly had to look believable, and they did that. Same thing with Sam Raimi's Spider-Man.