WWE is so often a business built on momentum. You can see that with things like Bryan winning at Mania 30, or Seth Rollins getting the title nod at Mania 31. Going with the flow makes sense, especially at a night like WrestleMania when it is all about giving the audience a final payoff. For Dean Ambrose right now, his momentum makes him the favourite for the Brock Lesnar match. He's had a big surge in popularity recently, with ever increasing noise for his crowd reactions. WWE will have picked up on that, they'll have identified him as arguably the biggest fan favourite in the company right now. Capitalising on that momentum will give the company a bold new star, as well as giving WrestleMania its feel good moment of the night. Many fans had wanted Ambrose in the main event title spot, but beating Brock Lesnar on the biggest stage of them all is more than a sufficient substitute. April 3 is the night when Dean Ambrose's momentum and potential will be realised.