Administrators in VA are regulated by the Commonwealth of VA not the federal government. Testing on a national level will not ensure quality administrators for this state.
Quality administrators, whether it is because of expense or fear of testing, will leave VA and go to neighboring jurisdictions. Also, there will be a lack of quality people coming to VA to practice due to stringent licensing requirements.
Only two states require a national exam. A third tried a national exam and changed to a state exam.