Feedback from the potential employer would be very helpful, but it rarely happens. Usually there is no reason given for a rejection, so the recruiter probably will not know why. Often the recruiter may not know the specifics of the job. Often the job description is not written by the actual manager looking for an employee, but by HR, so the job description may not be very accurate. This happens a lot, I found out.
I worked as a recruiter in the past. These are human relationships at work, disguised as a logical system.