One factor that's important, besides the boxoffice, is how the studio perceives the movie in terms of qualify and popularity. The movie "Superman Returns" is mentioned several times in this thread. I think the studio executives were not exited about that movie and moviegoers reactions were lukewarm (e.g. 6.2 rating on imdb). So despite solid boxoffice numbers they didn't do any direct followup to that movie and eventually did a reboot several years later.
I think two things hurt the film here in the States:
*Not using Khan in the marketing.
*Having such a widely varied release with the U.S. being later in the game.
But it is a very, very good movie.