Why would a voluntary certification standard be inappropriate for licensure?
A certification exam is designed by people who are already certified. You can think of voluntary certification like a private club and the members of the club get to decide what standard people need to meet to join their club. Club members are entitled to decide who gets in to their club and who doesn’t, they set their own policies and prices but they should not have the right to decide who can be eligible for licensure based on their private decisions.