Recent studies indicate that divorce rates are higher at lower educational attainment and lower income, for whatever reason. (In addition, divorce itself tends to be bad for the finances of the ex-spouses.) To the extent that divorced spouses are often uncooperative with each other, that can make the CSS NCP Profile a barrier to many students with such parents, even if the parental finances are otherwise quite simple.
So it is likely that the use of CSS NCP Profile screens out a higher percentage of first generation and lower SES students than it does for higher SES students.
The University of Michigan does require the CSS NCP Profile.