the 50:50 ratio is taken to mean there are no inhibitions or advantages for one or the other as this is the rough ratio of male to female in the general population. The skew of the ratio can be read as there are some factors we aren't seeing. So the question isn't "why do we need this ratio" but "why isn't this ratio present?"

No one cares who writes their code either, but certainly we can agree that if there are systematic reasons preventing women from participating as much we can try to remove them?