Why are these matches considered to be the best matches in Chinese astrology?

Rat man - Dragon woman
Ox man - Snake woman
Tiger man - Horse woman
Rabbit man - Sheep woman
Dragon man - Monkey woman
Snake man - Rooster woman
Horse man - Dog woman
Sheep man - Pig woman
Monkey man - Rat woman
Rooster man - Ox woman
Dog man - Tiger woman
Pig man - Rabbit woman