Men usually have more muscle, and more oxygen is required to sustain those muscles, something not to be taken lightly when your lungs are plastered against your seat (shakiness of a hand due to oxygen deprivation can literally be life or death for a pilot). This, combined with the fact that women have shorter torsos means the distance between the brain and heart is shorter and the heart doesn't have to work as hard to push blood up to the brain. The shorter torso / longer legs also means a smaller percentage of the pilot's body (and blood) is under the full gs, which also lessens the load on the heart. So a combination of these things makes women better at sustaining and enduring high g maneuverers. A man who happens to be short with a short torso and long legs has the same advantage, but it's uncommon, the same way a women with the required strength/endurance for infantry is uncommon.
Men usually have more muscle, and more oxygen is required to sustain those muscles, something not to be taken lightly when your lungs are plastered against your seat (shakiness of a hand due to oxygen deprivation can literally be life or death for a pilot). This, combined with the fact that women have shorter torsos means the distance between the brain and heart is shorter and the heart doesn't have to work as hard to push blood up to the brain. The shorter torso / longer legs also means a smaller percentage of the pilot's body (and blood) is under the full gs, which also lessens the load on the heart. So a combination of these things makes women better at sustaining and enduring high g maneuverers. A man who happens to be short with a short torso and long legs has the same advantage, but it's uncommon, the same way a women with the required strength/endurance for infantry is uncommon.