#2 To reunite The Club since he's injured
In the latest WWE NEWS, there were reports earlier in the month stating that AJ Styles was on a brief hiatus in order to deal with some nagging injuries. Now, we all know that nagging injuries are a part of the business and that every wrestler at some point works through them.
In the case of AJ Styles, it seems as though WWE decided to reunite him and The Club in order to protect him and prevent him from getting too physical on live television. That would certainly keep him fresh for PPVs.
Since he has now reunited with Gallows & Anderson, we can probably expect AJ Styles to get less physical and wrestle relatively lesser on free television. It would help him in the long run, but it does bring up the question as to what these "nagging injuries" are.