Someone mentioned this already -- maybe Hat -- but one reason is because a) she's a good coach, but also b) when she started no one really devoted much to women's basketball. They aren't as many teams at the top, and she was able to build a program without major competition for players or resources.
Women's sports always lend themselves to a dominating presence at every level. It's far easier to separate yourself...in golf, tennis, basketball, or anything else.