In Loco Parentis
With the July 1, 1971, ratification of the 26th Amendment lowering the voting age to 18 from 21, the process began at the various levels of government to lower the legal age of adulthood from 21. Before the lowering, schools with students between 18 and 21 (depending on the given State's laws) could be and were expected and required to act in loco parentis. In other words, since the founding of the Republic, colleges and universities were legally on the hook for their residential students just as if they were the students parents. So, yes, there were many and various good (legal requirements in some cases) for Fundamental schools to have what today are seen as seemingly pharisaical sets of rules. They are better viewed as paternalistic. Remember, in many States, you still needed your parents permission to marry if you were under 21. If you were under 21 you could not enter into a legal contract (enroll in college or university) without your parents' permission.
No, Dr. Bob Sr. did not pull them out of his ear. They did not appear ex nihilo at the founding of Bob Jones College. The demerit system has a long and honored tradition in US higher education. This is especially true for schools which see leadership traing as part of their mission. thanks in no small part to the US Military Academy at West Point and its follow ons the Naval Academy, Virginia Military Institute, and the Citadel.