Companies with at least one female director had better returns for six straight years. Which raises the question: If the financial argument for gender diversity is so compelling, then why aren’t companies recruiting more women to their boards? Or, to put it more broadly, why do public companies need an incentive to do something that is clearly in their own interest?

One solution to this dearth of women may be demographic. As more women graduate from college — in most advanced economies, their graduation rate is now higher then men’s — eventually more women will find their way to boardrooms and corner offices. Except that this isn’t necessarily true. By 2035, studies show, women will still be underrepresented.

In Silicon Valley, again, the shortage is even more acute. Only 20 percent of computer-science grads are women, down from 37 percent in 1985. The proportion of women in computer jobs declined to 27 percent in 2011 from 37 percent in 1990. Overall, women make up almost half the workforce. Yet they aren’t choosing careers in science, technology, engineering and math.