..Because he has made some high-class, fan-[censored]-tastic music from the Star Wars (even those crappy prequels), to Jurassic Park, Schiendler's List, Indiana Jones, and so forth.
I love his music. It elevates even the most crappy movie, and is part of why I don't mind the Star Wars prequels too much. Anakin and Padme can do whatever pieces of cardboard do in those Naboo scenes and I still think the romance in Ep II kind of works because of his 'http://www.youtube.com/watch?v=9nk_WHHTQtY' theme.
Other than film scores he also composed the theme for a couple of Olympic games, 1984 and 1996 if I'm not mistaken. The http://www.youtube.com/watch?v=YWdOFgDQIn0 is one of my favourite pieces of music ever, along with 'The Empire Strikes Back's 'http://www.youtube.com/watch?v=DvvK4CJ7CVU'. It's one of those pieces of music where you're hooked for the whole thing once you listen to ten seconds of it.