
It is pretty straightforward economic self interest. I can recommend Sowell's book "Charter schools and their enemies" it lays out the setup quite well.
1. Using only these scores would boost the proportion of elite university places awarded to Asians, who are already 'overrepresented' relative to their share of the population. Propel state various reasons why this is undesirable (equity/diversity, don't want everyone on campus to be 'the same') and unstated reasons (racism against Asians).
2. Blacks and Hispanics are 'underrepresented' at elite colleges relative to their respective shares of the population. The argument here is that these outcomes are prima facie due to 'systemic racism', i.e. not necessarily overt racist acts, but things in the system that together result in worse outcomes for certain ethnic groups.
If you want to read more about these topics, a few starting points:
1. Recent news (and Twitter discussions) about the University of California dropping the SAT.
2. Recent news about Lowell High School switching from partially-merit-based admission, to lottery-based admission. (And the court order from a few days ago, declaring this switch null and void.)
3. Thomas Sowell's books 'Economic facts and fallacies' and 'Charter schools and their enemies'. One of the points in these books (which include data) is that, when you adjust for things like parental educational level, number of parents in home, differences in outcomes between ethnic groups' career success often lessen or disappear altogether.
https://www.amazon.com/Charter-Schools-Enemies-Thomas-Sowell...