More Sex, Less Marriage
Prior to the sexual revolution of the 1960's, most women would not perform oral sex, and many, if not most, men never experienced it in their entire lifetimes. In those days many men divided women into two types: those you have sex with and those you marry.
Fast forward 50 years and we see women have changed. Now oral sex is about as common as shaking hands when meeting someone. So now there is only one type of woman. Is it any wonder marriage rates have declined?