The comment above is getting downvotes, but it isn't implausible. The western world has seen declines in sperm counts, testosterone, and age of menarche.
We don't know the cause, but environmental hormonal causes are one hypothesis.
Here's one aspect: https://en.m.wikipedia.org/wiki/Testicular_dysgenesis_syndro...
It's easy to see how lower testosterone would lead to less sex. It is very unlikely to be the only cause, but it likely has some impact.
the chemical environment people grow up in today is different from the one 10 years ago, or 30 years ago, etc.
we may very be improving in some dimensions -- like removing lead -- while getting far worse in others (plastic and anti-androgens).