"Why can't they come up with something original?"
My take. Because the suits that decide such things are devoid of any imagination and creativity - for the most part.
To increase the chances of a film to make money, they rely on big budget actors, directors, music composers, special effects, car chases, action sequences, explosions, etc. They often use a lot of the above to hide a weak story knowing much of the mass audience doesn't know the difference. Many films today, especially from the big studios, are constructed this way to maximize profits, but it all comes down to the screenplay and how well the director communicates it to the audience, with or without big budget stars.
Bullit sorta falls into that category. The story is a little weak, but the movie ends up a cult favorite due to the chase scenes and the fact it starred McQueen. A "few" comments about the film.
http://www.imdb.com/title/tt0062765/usercomments
Sherwood