It is thought that including adult material could prevent films achieving a family-friendly certificate, restricting a film's audience and box office potential, the Independent reported.
Vincent Bruzzese, president of the film division of market research company Ipsos, told the Sunday Times: "Sex scenes used to be written, no matter what the plot, to spice up a trailer. But all that does today is get a film an adult-only rating and lose a younger audience. Today such scenes are written out by producers before they are even shot."
In this year's crop of Best Picture nominees at the Academy Awards, Django Unchained caused controversy with its violence and language, while Zero Dark Thirty came under fire for its depiction of torture.
But there were no explicit sex scenes, even in Silver Linings Playbook, in which Best Actress winner Jennifer Lawrence plays a sex addict.
A recent market report for Warner Bros suggested that while female cinemagoers enjoy seeing handsome male actors on screen, they're turned off by sex scenes that do not serve the plot.
The British Board of Film Classification confirmed that in the UK, the percentage of adult-only movies dropped from 12 percent in 2001 to 8 percent in 2011.