The average employer could just look at SAT scores and hire HS graduates with good ones, train the employees on the job and all would be well on their way to mutual success.
Companies used to give $50 IQ/Competency tests to decide who to hire. When that became illegal they went to only hiring people who had degress as the next best way to judge an unknown quantity. Now that everyone has a degree they only hire people who have degrees in a good major or from prestigious schools.
Since the courts have decided that disparity equals discrimination your method would get a company sued for not hiring enough blacks.
I’d go to MIT for an engineer, rather than to the SAT scores, but I agree with you for a lot of jobs. Many car rental companies only hire college graduates not just for accounting but even for taking reservations and working the rental counter. I find it amazing that someone is spending $200k for four years at a private college, and their dream is to take that Elizabethan Literature degree or Gender Studies sheepskin to the Enterprise rental counter? I also find it amazing that my local car rental company would rather have someone with those degrees than someone motivated and ready to do productive work right out of high school.
Employers are NOT ALLOWED TO.
Since some Supreme Court decisions back in the 1970's (a decade full of bad SC decisions), notably the Duke Power decision, employers are not allowed to use written tests in their hiring decisions, where such tests have "disparate impact" (more blacks getting low scores than whites).
Prior to that point, employers would take people out of high school, give them some tests, and assign them in the company accordingly.