Die Hard was the first film in what would become one of the most popular franchises of the last three decades. A massive commercial success, it also created a set of expectations for the career of Bruce Willis: people expected that his every new film would start a franchise. From Hudson Hawk on, through The Last Boyscout and Striking Distance, every film was supposed to be the foundation of another great franchise.
But these other characters did not have the staying power of John McClane. It turns out that the same shit tends to only happen to the same guy once when it comes to successful film franchises (unless that guy is Harrison Ford, obviously).