Foi uma decisão do diretor, George Roy Hill :
Hill decided on a contemporaneous score for his film in lieu of a traditional Western approach, as he wanted the music to match the demeanor of the two principal characters. As such, Burt Bacharach, who was a pop icon at the time, was brought in to score the film. The score was constrained from the onset as director Hill did not want music to play during scenes with dialogue. Lastly, he and Goldman decided that three musical interludes would be inserted into the film. So of the 26 minutes of music Bacharach wrote for the film, in the end, only twelve minutes of music was used! For the songs, Bacharach brought in lyricist Hal David, and for vocals, B. J. Thomas. Early on, Bacharach understood that the film was character driven and so his music needed to speak to the dynamics that existed between the three main characters.
Outro artigo sobre o assunto afirma mais ou menos o mesmo:
Director George Roy Hill didn’t want to make a typical Western, and the script by William Goldman doesn’t rely on tried and true Western cliches while Conrad Hall’s cinematography plays with light and color. But the choice of Bacharach to write the score was arguably the director’s most controversial move.
Hill made it perfectly clear from the outset that he wanted the music to have a semi-contemporary sound and not a traditional symphonic Western score. He also wasn’t fond of scoring dialogue sequences. Hill decided in conversations with Goldman that there would be three musical sequences. The music is spotted so sparingly that it totals a whopping 11 minutes of music. (The album contains much more music than is heard in the film.)
Bacharach said in an interview,
George wanted [the score] to be special. When it was used, it was to have a real … important place… It wasn’t to be filler music, it wasn’t to help the story along … It was to have importance.
No entanto, parece que o diretor não foi imediatamente vendido em todas as ideias :
In the summer of that year, Bacharach was writing the score for Butch Cassidy and the Sundance Kid, a film starring Paul Newman and Robert Redford as 1890s train robbers. Director George Roy Hill wanted something evocative of the period for a particular scene where Newman takes a romantic bike ride with Katherine Ross. Though Hill was initially opposed to the idea of a pop song with a lyric, Bacharach talked him into it.