#4 As a "thank you" for his years of service
R-Truth has been around a lot longer than most people realize. He was with the company between 1999 and 2002 and returned six years later, and has been with the company since. That means that he's been in the WWE for a whopping 14 years.
Not many superstars get to say that they've been with the company for so long, and it's clear that Truth is well-respected backstage, even among the McMahon's. After all, he does make Vince McMahon laugh more than most people can, so what's not to like?
Corey Graves deleted his Tweet! More details HERE.
He's been around for a very long time, has been a part of all sorts of storylines - whether it was his serious persona, ridiculous storylines, tag teams, etc. he's never complained and has always known his role well.
With respect to that, it's likely that WWE wanted to give him a small run with the title as a token of gratitude for all his years of service.