Japan’s birth rate has been dropping for decades now, and while it’s possible the demographic shift is a result of couples just getting that much better at using contraceptives, you have to allow for the possibility that fewer babies is due to fewer couples doing the deed.
Lending further credibility to this explanation is the fact that the proportion of Japanese men in their 30s who still have their virginity has gotten so high that society has coined a new slang term to describe them: yaramiso.