Genetics. Sorry. However, no one that I coach trains a bodypart one time a week. As I coach throwers, pl'ers, and Ol'ers, most of the focus is on the legs and back, and some throwers will be training their back four times a week, but different parts.
I will say that the focus on strength as a goal seems to work better for women who wish to gain mass. Without wasting time on "shaping" movements or worry too much about staying lean, it is easier to focus on the big lifts, which is pretty much what everyone should be doing.
Spatts posted her new training split, which is remarkably similar to the one I use for pl'ers.
OL'ers will train up to ten times per week, with each training session focusing on aspects of the contested lifts in the morning, and heavy assistance work in the evening. Example:
Monday: AM: Heavy Snatch, light clean. PM: Heavy squats
Tuesday: AM: Heavy clean, light snatch. PM: light front squats and more pulls(such as RDL's) if bar speed is weak off of the deck.
Wednesday: AM Heavy jerks, specialized assistance work
Thursday: AM: Heavy Snatch, light clean. PM: Light squats.
Friday: Heavy Clean, light snatch. PM: Heavy front squats, more pulls if necessary.
Saturday: Heavy Pressing and assistance work.
Note: The AM sessions will also involve specialized assistance work such as power versions of the snatch and clean, which are sometimes substituted for the light versions of same, as well as snatch and clean pulls. Reps are low (less than five) on all exercises, and on heavy cleans and snatches, never exceed two, but mutilple sets will often be performed. In the evening sessions, reverse hypers or ham-glute raises are done, with abs being worked specifically twice a week, generally on Wed and Sat.
Also, most of these women are throwing, or performing some other sport. Variations of the above included subsituted heavy inclines for shot putters and javelin throwers, and limiting the jerks and heavy presses, which are less specific. And most of the snatch and clean work functions as active recovery for the heavier movements, such as squats, snatch grip deadlifts, rdls, good mornings, etc.
And they get to eat as much as they want, usually for free. The joys of an athletic scholarship.