It could have been a lot of nudity, violence or both and that appealed to a wide audience. No one went to go see Basic Instinct or Rambo for the acting. Movies were about entertainment and no one was pulling any lunches. Then, it all changed.
Movie theaters started being located in malls and the audience shifted. Adults were staying home and watching movies on television or renting and it was the teens that were filling the theater seats. They were at the mall anyway hanging out, so why not just go see a movie. They were too young to watch rated R movies and mom and dad were nowhere to be found to offer permission.
Studios started losing money on R movies, so they were dumbed down to meet the ratings for teenagers. Movies that deserved R-ratings were stripped of violence and language, so they could get that all power PG-13: the perfect demographic. For adults, this era of blockbuster movies is dismal. If you want something R-rated you almost need to watch straight to video or independent movies that don’t’ go to the theater.
As a fan of the R-movie, this current climate is a tragedy and some great movies are being castrated so they earn maximum profitability.