Was it even a real thing considering the few female warriors in history. Are the cups really necessary or just a visual stimulus for men in movies?
u/sunagainstgold and I gave some examples in the thread on where did the trope of "Boob Armor" originate? which might answer your question.
They didn't need to. Plate armour is generally designed with ample room for padding underneath, and usually shaped so that strikes are deflected down and to the sides. So even men's armour usually has ample room in the chest area.
Taking a hit in tight fitting plate armour from a heavier weapon like a mace or hammer would almost be as bad as if you took a hit completely unprotected. The point is to create a gap that allows the springiness of the armour and the padding underneath to dampen and distribute the force of the hit.