you typically ask the other person about stuff that matters to you on the first few dates. if you’re a few dates in and a man asks what your body count is, it is safer to lie if you have a high body count. based off his reaction (or even the fact that he’d ask) then the person can decide for themselves if they want to continue interacting w that man.
I wouldn’t consider the relationship to be built on lies just because of a made up number for a body count. Because to me that’s not a lie about anything that’s actually important, and a relationship isn’t built based on each other’s body counts. I agree that lying to your partner in general is bad, but for this specific topic I just don’t see it as a big issue. Truthfully, the topic shouldn’t even come up so I agree with you on your last sentence.