>>719933468
They were desperate to get anyone that fit the right genetic markers and potential physical opportunities for getting the augmentations, and gender didn't mean anything. For the SPARTAN-IIs, they kidnapped children from their families and left flash clones in their place to die of illness within the year, making child soldiers into superhumans. For the SPARTAN-IIIs, it was more volunteer, but still needed to pass the rigorous requirements for lower quality augmentations and equipment..
The future of warfare doesn't care much for race or gender if everyone is just as viable for putting a bullet in someone's head and your entire intergalactic military-government hybrid faction is at risk of pulling itself apart if more insurgencies and insurrections happen across its vast array of planets at its fingertips. And that's before the Covenant showed up.