@Su_GProbably because that would open another can of worms. Yes, women pay tax at the same rate as men on paper but in reality the total amount they will pay over their working life will on average be less due to the fact that on average, women earn less than men.
The financial argument isn't the best one in this case. Medical care should be according to need, not the ability to pay.
The simple fact is it's discrimination, which in the EU, and UK is unlawful.
@Gina