Why are martial arts experts rarely women?

Not exactly. It's all because women are going to have children. Another point is that the meridians for practicing kungfu are somewhat different from the female physiology. Because women will get married sooner or later. But after practice, women won't have children. Therefore, most people who know kung fu are men.

There are many historical reasons that I won't introduce here.

Isn't Wing Chun very good now?

Girls can learn.