#2. It's the only way Daniel Bryan could get the upper hand
Daniel Bryan challenged The Fiend to a strap match last night on SmackDown, but in order for Bryan's narrative of the situation to work, The Fiend needed to run away from him, which meant that Bryan needed to sneak up on Wyatt and gain the upperhand.
Bryan would have found it hard to sneak up on a man who literally lives in the shadows, so calling in someone like Kane who Bryan knew The Fiend had a history with was the perfect way to ensure that he would be drawn out and it meant that Bryan could attempt to weaken his opponent ahead of their showdown next week.
Bryan's plan worked since Kane was prepared for the attack and Bryan was in position to take advantage. Perhaps even more shocking, The Fiend actually accepted the challenge for a Strap Match at the Royal Rumble next weekend. So regardless of what happens, he will be forced to stand and fight against Daniel Bryan.