???
The "sexual revolution" was in the 1960s. This drop in births started in the early 2000s.
Men haven't changed. Women did.
Feminism didn't free women from the oppression they were told they were under, it freed men from the oppression they didn't know they were under.
After generations of lies and indoctrination through government education and the Propaganda Media, social media showed men just how badly they were being screwed. Once women went online and showed their true selves, men starting walking away.
I have only seen men get worse, since the 1960s. They took the supposed ‘freedom’ of birth control and ran with it. They expected women to put out on the first date, still do, and they were not interested in a woman who expected them to wait until marriage. There were plenty of willing women, so they could just move on to the next.
Most haven’t backed off from that.