#2 Because of the history that Paul Heyman and Roman Reigns share
Roman Reigns was involved in a long and interesting rivalry with Brock Lesnar that stretched out for many months. We all remember the segment on WWE RAW, where Paul Heyman sprayed Roman Reigns in the eye with mace. And one has to believe that from a storyline perspective, this is the point where Roman Reigns developed a deep admiration for Paul Heyman and his methods. And it was because of the same that Roman Reigns decided, on one fine day, to become a client of the man who refers to himself as 'The Advocate'.
Look at how many former Champions have been 'Paul Heyman guys'- from CM Punk to The Undertaker, from Brock Lesnar to Stone Cold Steve Austin.
At the end of the day, you make a deal with the devil when you want riches and success beyond comprehension. Roman Reigns and Paul Heyman have signed a pact and the future is going to be very interesting for one and all.