#1 To end the night on a cliff hanger

WWE changed the match stipulation between the team of The Undertaker and Roman Reigns and the team of Shane McMahon and Drew McIntyre from a normal tag team bout to a No Holds Barred match within a week. WWE creatives do not go for such a change quite often unless they have something in their mind. It is quite probable that the bout would not end in a clean fashion.
It is a known fact that WWE is apparently struggling to maintain their TV ratings. WWE needs to build a proper storyline before SummerSlam and at the moment, WWE does not have much to go by. Thus, ending Extreme Rules with a brilliant cliff hanger would not only help the PPV garner better reviews but also would make the fans tune in to watch the next episode of RAW.