The article starts with " In the United States, of 500 doctorate degrees awarded in economics to US citizens and permanent residents in 2014, only 42 were awarded to African Americans, Hispanics, and Native Americans and 157 to women (although this double-counts the 11 minority women who earned economics doctorates in 2014). "
There are about 1100 students who receive their PhD in the US (see NSF report) of which about 33.4 are female, about the same percentage as for US citizens and residents.
It seems that Econ is doing much worse than many other fields (see Figure 1 from their paper below, where Economics (E), Humanities (H), Social Science (SS) Business (B) STEM (STEM)
Thinking about why women are not becoming economists, they write:
Performance in early economics courses—such as introductory courses—and especially relative to performance in other courses may also be related to the decision to persist in economics. Rask and Tiefenthaler (2008), using 16 years of data from a liberal arts college where economics is a prominent major, find that women are more responsive to their relative grades in economics than are men. Of course, if this response exists across economics departments, it is likely related to the specific context of economics, including advising practices: if women were universally more responsive to relative grades, then they would also be more averse to majoring in math and science, where grades tend to be low (for example, see Butcher, McEwan, and Weerapana 2014, in this journal), but where female representation is higher than in economics."
Being economists, they also have a section on why it may matter why there are no women and minorities.
"First, opinions among economists about policy are not the same across different groups. In a survey of 143 AEA members with doctoral degrees from US institutions, May, McGarvey, and Whaples (2014) find that male and female economists have different views on economic outcomes and policies, even after controlling for vintage of PhD and type of employment. For example, relative to male economists, women economists are 21 percentage points more likely to disagree that the United States has excessive government regulation of economic activity; 32 percentage points more likely to agree with making the distribution of income more equal; 30 percentage points more likely to agree that the United States should link import openness to labor standards; and 42 percentage points more likely to disagree that labor market opportunities are equal for men and women."