#1 Make Braun Strowman look good at Backlash
It's no secret that Braun Strowman is an absolute Monster Among Men, especially after flipping over semi trucks and demolishing a ring in a match with the Big Show, which is why the company now needs to stack the deck against him. At least that way, it puts Strowman in a situation where he can't just rely on his strength at Backlash. He will also have to watch his back as well.
If nothing else, this should lead to some very creative storytelling inside the ring between the three Superstars and could serve to test the limits of Strowman as well. In fact, WWE almost seems to be putting him in a do or die Superman situation here and this could be a way to establish him as the next top guy.
Whether that actually happens or not remains to be seen and will depend on what the company is thinking, but there is a case to be made for this being a way to make him the top guy. Either that, or WWE is just looking to create reasonable doubt during one of their B level pay-per-views and plans on changing nothing. Regardless, a win over Miz and Morrison at Backlash will do wonders for his title reign.