#2 It's already served its purpose
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Although it is pretty obvious that The Shield reunion is beyond repair at this point in time, WWE can b= rest assured that the angle already served its purpose and was effective in doing so. Of course, that purpose was to put over Roman Reigns in a way that fans originally thought impossible, but by the looks of the crowd reaction, they're really into him now.
Who knows why that is exactly or how long it will last before The WWE Universe ultimately turns on him for the 100th time, but that doesn't mean WWE didn't do everything they could in trying to make this work. In the end, though, keeping The Shield together will not only be a huge disappointment for fans, it will also be overkill at this point in time.
If nothing else, WWE needs to understand that The Shield reunion, no matter how brief it was, helped get Reigns over with the fans and is no longer needed in order for him to be a popular star. They also need to realize that keeping The Shield together would be distasteful at this point and would only serve to be a shell of what it really could have been.
Take the win and go home WWE!