Star Wars and rating system. Star Wars changed everything, the way people viewed movies, the budgetsspent on movies and the way Hollywood made movies, while on its own this did not hurt S&S Cinema it set the stage for its decline, focus moved, Star Wars became a benchmark standard.
You also had the changes to the rating system, R and PG movies were made into PG-13 movies, then NC-17, with clearly defined restrictions on violence and sex, up to this time S&S had a good dose of both, then as said it was defined to violence and simulated violence (no blood).