Why do female gymnasts have a bulge in the crotch area?

You are talking about the way a woman's pelvis looks. A woman's pelvis rises higher than a man's pelvis. That's just how women are made. That's probably because women have to give birth. There needs to be plenty of room for the baby. If you could push a woman's pelvis down closer to her body and make it look more like a man's pelvis, then there would be less room for the baby. She would probably need a C-section in order to give birth because the opening for the baby would not be large enough.