The thing that primary predicts less teenage sex is sexual education. Which is better then used to be.
The conservativism of parents where you lived likely contributed to kids having sax in the park hoping nobody will arrest them and charge them with public sex.
And honestly, I never witnessed what you described here and I am kinda happy I did not.
Given that teenage pregnancies are also down and so are std and so is drug taking, yes. And given how much of effort was put into making teenagers have less sex and use dammit condom, yes.
Because side effect of that period were teenage pregnancies that had quite destructive effects for the rest of those kids lives. And side effect of sexual education are safer sex practices.
On the second point, that is actual risk involved. I would not made those laws, but I can't change them.
Third thought, it is also not comfortable to lie in park without things like blanked under your body with guy focused on finishing as fast as possible. I don't know how to tell it differently, but in average case the girl won't have that much fun in those quick minutes as guy who has fun until he finished. Which means less drinking and drug taking must be factor in drop of those encounters too, because one of partners would be more likely to refuse the activity.
The conservativism of parents where you lived likely contributed to kids having sax in the park hoping nobody will arrest them and charge them with public sex.
And honestly, I never witnessed what you described here and I am kinda happy I did not.