I know it sounds like a joke, but I'm serious. Dana recently reopened conversations with both fighters and both left the sport disgraced for steroids. Jon Jones even called out Brock after his last fight, despite Brock getting popped which means JJ is willing to move up in weight. JJ may have even been subconsciously hinted at his own steroid usage by calling out Brock.
Besides no one is ever going to trust them to step into the Octagon clean. Makes sense to let the cheaters face off. All the mms fans will know what it is.