[burnished]

Disclaimer: keeping situations that are clearly criminal 'in house' is bizarre and I agree - forward to the authorities. Many situations fitting the mold of this article are not so cut and dried so I am primarily addressing that here.

Well, from a practical stand point not every instance of inappropriate behavior is illegal, and not every instance of illegal behavior is prosecutable. If you want standards for behavior in your group you probably have expectations of time to resolve and level of evidence than the legal system is not going to meet.

From a more philosophical perspective it would make sense for groups to form and enforce norms - the law sets a minimum expectation of behavior after all and has very different goals/principles. A legal system might err on the side of leniency/underspecifying in order to preserve liberty, and have requirements around process and evidence in order to put constraints on the authority to put a person into a cell for the rest of their life. Rules around who can attend a tournament don't have the same scope or impact and are probably not improved by including the assumptions of the legal system.

From a pedantic standpoint they are not at all creating another legal system because they have precisely zero authority, they are enforcing social norms through freedom of association. That you might see similarities probably isn't surprising given the need to investigate claims and take action, especially given the increased desire around transparency and hence published standards.

Side note; I feel your core observation but I personally wonder how much is something new vs a function that has broadly existed in organizations that is becoming visible due to expectations around transparency and action.