Before the Marvel Cinematic Universe launched in 2008 with the release of Iron Man, the movie rights for the character were turned down by New Line Cinema, which had acquired the rights from Fox in 2000. According to a Hollywood Reporter source, New Line opted not to pursue Tony Stark’s story because Bob Shaye, who ran the studio at the time, argued “that it didn’t make sense because Iron Man was too heavy to fly.”
Although the project was already in the early stages of development, New Line let the rights expire. Marvel reacquired them in 2005, and today the MCU has banked $27.4 billion at the box office.
Source: New Line Cinema Abandoned Iron Man Movie Because He ‘Was Too Heavy to Fly’ | Complex