Colleges base their admission decisions on a variety of different criteria. One of them is how well the student can write. At present they have two ways of measuring that, neither of which is worth much.
One way is by the SAT writing exam. The problem is that consistent grading across a large number of students requires something close to machine grading, human graders checking the essay against a simple and objective set of criteria. That might tell you how well the student has trained for the test but it is not very good evidence of how well the student can write.
The other way is by having a prospective student send in an essay for the admission people at the college to evaluate. However good a job they do of evaluating the essay, they have no way of knowing who wrote it. The applicant may have written it entirely himself, he may have written it himself and had it gone over by someone more expert in writing, he may have hired someone to write it for him. I have no inside knowledge, but given how important college admissions have become I would be astonished if no such market exists.
There is a simple solution. Many applicants visit a college before applying. As part of the process, put the applicant in a room with a computer and a list of topics and give him an hour to write an essay. If the applicant is not going to visit the college, perhaps there is an alumnus living near him who would be willing to provide the computer and monitor the writing. If multiple colleges want applicants to write essays under controlled conditions, it should be in the interest of someone, perhaps the organization that now administers SAT exams, to arrange suitable facilities in cities scattered across the country.
It seems like an obvious idea and I do not know why, so far as I can tell, it has not yet happened.