> I'm assuming it doesn't mean being capable of basic sexual activity, because that seems like a given for 90% of potential couples

I would suspect that more than 10% of women complain about a male partner being unwilling to perform oral sex on them, or bad at it, even though this might be very important for them and the main way they can orgasm. Men, too, complain about women’s ability or receptiveness to things they need for satisfying sex.