So if you have 3 students from the same high school applying to the same “test optional” college, and 2 have taken the SAT and done well, what is the motivation for the college to accept the one who did not take it at all? Assuming that GPA and other qualifications of all 3 were about the same. As an applicant I would not feel competitive in that scenario if I was the student who opted out of the exam.
I think it is a risky way to proceed, especially for the more competitive schools where the pool is strong. Strong students are not going to shy away from standardized testing.