Why won't a poor high-SAT-score, future STEM graduate be able to get a loan? Banks will mostly take into the account the probability of loan repayment, not how poor the person is right now.
People from poor families drop out at a higher rate than non poor family peoples, as well as carry over lower average earnings and a higher likelihood of defaulting on loans even after graduation. A single generation getting a diploma will not equalize the gap between poorer and richer families.