The Iron Giant was a literal box-office failure upon its initial release back in 1999. This was due to Warner Bros. not realizing what an exceptional film it was and not promoting it accordingly. It is a good movie that accurately portrays the national mindset about outsiders. It shows how a new generation can teach us all about violence and discrimination.
"Friends" is a stupid show. And everything about the show and its cast members is straight up dumb. JK (though I hate "Friends"). But seriously, like any movie, it wasn't that big at the box office. A lot didn't see. It was one of those movies that was tossed through time.
No one even remembers it today.
No, Iron Giant's failure was not due to subject matter. It was a strange concept that did not appeal to the masses. Although a smart and creative concept, Iron Giant's failure was due to lack of appealing illustration and an engaging story. It is not the type of movie children or adults would enjoy.
The film now has almost a cult following. I think it's not the subject matter, but more the lack of marketing, and mabye the timing of it's release. Many blame Warner Bros for failing to promote The Iron Giant - since The Quest for Camelot was so badly received the studio wouldn't give Iron Giant a release date. They were shocked with the film's reception by test audiences and didn't do any food/marketing tie-ins or any type of publicity blitz when it finally hit theaters.
I don't think it was the subject matter as much as it was the marketing campaign that caused the box office failure. Some movies just don't get pushed hard enough to make it into the public eye and cause a massive buzz. This was one of those situations. The movie ended up being a favorite, but it didn't do well at the box office.