My bet it was always enforcement by gaslighting. Technically, current streamers can do collab stream with blacklisted terminated ones on their private account. And if niji terminate them for it, they can sue niji and will win. And even be restored in position for whatever was left of contract term in they choose so. (If there were no other valid excuses for termination.) There is no conflict of interest when it comes to doing shit on private accounts, so any judge will toss out any rules about them, if niji dared to present them in court at all.