Many people attribute "feminism" to be a contributor of the sexual revolution. In reality, however, feminism was a small contributor (if it was a contributor at all).
Women throughout history always had jobs in the workforce.
Some of these sex roles are arranged voluntarily, such as men instead of women typically driving cars. Men are not forced to do the driving by society, but in the marriage, the men and women come up with an agreement that the man should drive. Throughout much of history, women were not "forced" to do manual labor work. This is probably because women could get married and do housework instead. There were not washing machines, wrinkle-free clothing, dishwashers, and vacuum cleaners back then. Before the advent of technology, women did have a job. Also, before machines replaced many manual labor jobs, men were forced to do manual labor instead. Before machines, men, women and children all had to do manual labor work to earn a wage.
Technology had made housework easier, so women no longer have to do full-time housework. The result is that marriage at an early age has become less useful.
Declining birth rate
People were having fewer children, eliminating the amount of time necessary for women to stay at home to raise children, making the role of the housewife redundant.
With the widespread availability of birth control, women are able to have casual sex without fear of unwanted pregnancy.
Increase economic prosperity
Unlike third-world countries, women don't need a man to provide for her anymore.
Reduced the negative consequences of casual sex (increased disputes involving paternity). This relaxed the legal attitudes against infidelity.
Premature puberty has also made women more slutty. In the 1900's, girls typically had puberty at around age 14. In 2010, girls tend to have puberty at age 10-11. This means that their sex drive begins earlier, leading them to have sex at an earlier age. In 2010, women on average began having sex at age 15 rather than the 1900's where women had sex later because puberty occurs later. In the 1900's it was easier for women to be virgins until they marry at 22 years of age. In the 2010's, it's much harder both due to earlier puberty and later age of marriage (women in 2010 marry at age 26, allowing more time for them to be sluts until they marry).
Studies show that religious people are more against casual sex.
The majority of Americans are still Christian. This suggests that it was more of a moral shift rather than a religious shift. Nobody really follows the bible 100% strictly, not even in the past, so it was more of a moral shift (in addition to the technological and cultural shifts described above).
As you see, many of the changes throughout society (like women being sluts, women in the workforce, etc.) were not contributed by feminism.
Standards for modesty
Single women don't have boyfriends or husbands who tell them to dress modestly.
Maintaining a positive sex image wasn't taboo anymore due to the minimized consequences. Wearing makeup, buying clothing, etc. was stigmatized before birth control but not much after birth control as such behaviors are less likely to cause "immoral" sexual behavior such as unintended pregnancy and cheating.
Men also buy expensive cars to impress women.
Words like "badass" and "pussy" are used as praises and insults. "Badass" is attractive to women. But "pussy" isn't attractive to women. Why are such words used more often? It's due to our increased obsession with maintaining a positive sexual image.
Women put on makeup and buy clothing in attempt to maintain a positive sexual image. Men work out to maintain a positive sexual image.