If the presupposition is that baby boomers were having more sex, and this I think is the central comparison, then perhaps the reason was that they felt far more entitled than their millennial counterparts: entitled to a good job market and secure class comforts, entitled to the spoils of their genders, entitled to have what they wanted from either people or culture. Millennials are hesitant. They are self-conscious. They cannot so easily walk up to someone and decide they will simply have them without confronting the complications of what they want and they feel. With human relations, things are more complicated when you do not feel like you can get away without thinking about them.