Why does Venus guard two constellations?

Specifically, the sun and the moon dominate the lion and cancer respectively, and then separate to both sides. Mercury dominates the two constellations on both sides of the lion and cancer, namely Gemini and Virgo, and continues to expand. Venus rules Taurus and Libra, and so on. Each of the five planets dominates two different day and night constellations, and only the sun and the moon dominate one constellation.