From the article:
We found no changes in low-income and underrepresented student enrollment after the colleges went test-optional. Instead, we found an unintended consequence of these efforts: Test-optional policies led to an increase in the number of applications overall. That necessarily forced the colleges to become more selective. That’s because more applications typically mean more rejections. More rejections make it look like the colleges are being more selective. That appearance of selectivity enables a college to claim a higher spot in college rankings that view selectivity as a good thing. This all creates a perverse incentive for colleges to go test-optional that has nothing to do with expanding access for students from low-income families.
We also found a 25-point increase in the reported SAT scores of enrolled students. This increase may be driven by higher-scoring students being more likely to submit scores to bolster their applications. Meanwhile, lower-scoring students keep their scores to themselves. This results in higher average scores being reported to the federal government and magazines that publish college rankings. Thus, it appears as though by increasing competition for a limited number of seats on campus and increasing the SAT scores used to generate college rankings, test-optional policies may actually threaten the very access goals they were designed to achieve.