Night of Joy is attended by a LARGE number of teenage youth groups with minimal supervision. Without sharing the stories that were shared with me, as some aren't even appropriate to share, they create a large amount of work for CMs who have to work it. CMs have stated they have to close some attractions for safety and remove some things from the park altogether. One CM said his full time job was to delete ride photos. There are plenty of posts (and I have also had them tell direct to me) that NoJ is the worst nights all year they have to work. There were even some blogs last year from attendees complaining about the teenagers behavior, the crowds and tempers lost.
Remember Magic Kingdom used to host Grad Nights and after 2011, Disney gave no real reason .... but am sure they had enough. Turning the park over to that many teens leads to behaviors, especially in attractions, where they think they are out of sight.
The true spirit of Night of Joy (Christian Music Concert) can be better achieved in a location such as WWoS where they can create a better concert environment with multiple stages, some under cover, food offerings that can be better managed and more control of behavior. The attendees will still get their MK ticket, but we'll have to wait and see if that is just for them to attend on the day of their choice that weekend - with other guests and if MK will have normal hours those nights.
The Disney Blog reads "Plus, dedicated transportation will be provided so that guests can easily move from Magic Kingdom Park to the Sports Complex." so I read that as if they go to the MK on the day of the concert, then there will be buses direct to WWoS to start the concert portion so they get there quickly without transfers. I don't read it that there will be buses going back and forth.