When you are the only true religion on earth that Jehovah has seen fit to use to announce to the world he's taking over by force, and that people need to join it and get baptized into it to be saved from a destruction that could happen anytime now,, you don't allow any debates because it will only cause confusion for the captive members and might start them thinking independently.
Seriously,,, the Governing Body don't debate they Listen & Obey, they don't question or research for facts, they accept all present Watchtower Corporation truths as printed never a debate they are all everyone of them corporation Yes Men who believe tons of fucked up shit to keep hold on to their positions.
Why would a bunch of uneducated corporate CEOs want to be found out(become public knowledge) how they vet a person to be a GB CEO like them. That's something you don't want the world or your members know.