Vince probably realized the only way Reigns was getting over was the Stone Cold route of beating him up, so he pulled the trigger quick.

I think it also was the only way to guarantee it would work. Avoid a smarky PPV crowd and get Raw fans excited at a world title change that none of them ever thought would happen when showing up at the arena. Now you have your coronation with an excited crowd and all of the images you need for video packages in the future.

I'm not calling this the best move WWE has ever made, but they polished the turd they gave themselves as well as possible.