William Friedkin on why Sorcerer failed at the box office
I recently watched the interview with Friedkin in the DVD extras for Bug, and one of the questions he was asked was why he thinks Sorcerer did so poorly with audiences after its release, given the success of The French Connection and The Exorcist.
His response was that the late 70's marked a sea change in what audiences were expecting for big budget studio films. In the late 60's through mid-70's, dark themes, slow pacing, and character studies were what people wanted. With the success of Star Wars, audiences increasingly wanted major studio films to be fast paced, escapist fluff, paving the way for an increasingly youth-market oriented entertainment industry in the 80's and beyond.
That basically mirrors my views of why the era of substantive big budget major studio films mostly came to an end in the late 70's.