Why are white women still the biggest beneficiaries of affirmative action?

In the 2006 book Legalizing Misandry: From Public Shame to Systemic Discrimination Against Men, the authors write, "Although polls have shown considerable American support for affirmative action, those who advocate equality of opportunity (even in a modified form) have criticized it for...conferring greater benefits on white women than blacks of either sex, for whom affirmative action was originally designed."