I was listening my local radio station and they had a story about how women were banned from speaking in public. One of the guest speakers (mostly, women from Afghanistan) gave a history of how it became like this.

There were freedom fighters, or Mujahideen, which were trained in jihad against the Soviets. And part of that indoctrination involved physical separation between males and females, including family members, of the boys and men that later became the Taliban. And part of that indoctrination involved the mullahs, or teachers in those seminaries, teaching or indoctrinating the students, all males, that females are the source of temptation to sinful acts.

There's more to it in the story / transcript, but that was the basic premise.