I wonder if that's due to an older generational perspective on sexuality, being tied more with reproduction? Like before Boomers was the Great generation and before that... I dunno, but I do think that people married with a thought to (probably) have children, or at least did so with much higher frequency than today.
So perhaps that's why we wouldn't think along those lines today, but they may have back then.
Why did I read this as "piss in it"?
Maybe that helps with understandability even... 🤔