The Solar 5th and 8th House

Some AZZtrology states that it's the 5th and 8th house that represents sex. Say a person has a Aries Sun, their solar 5th would be Leo, 7th be Libra, and 8th be Scorpio. Now we all know how opposite signs work, there is a lot of mutual attraction between any Sun sign and its 7th sign. Seeing as the 7th doesn't even represent dick and pussy, why isn't there the same kind of attraction for the 5th and 8th, the houses that are actually about dick and pussy?