The reason WWE decided to switch John Cena to the RAW brand and make him a free agent was because Vince McMahon wants Cena to help elevate and give the rub to Roman Reigns.
In addition to that, Cena will have fresh opponents to work with on the RAW brand such as Samoa Joe and Braun Strowman. Justin Barrasso of Sports Illustrated reports that current plan is to continue building up Cena with Cena being used to elevate Reigns in the end.
