The reason for the Shield’s face turn was because the New Age Outlaws wanted to work a program with them before they split the Hounds of Justice up.
There’s a plan for the Shield to split and creative thought it would help push Reigns as a top face if Ambrose and Rollins turn on him rather than Reigns turning on them. The plan is for Ambrose and Rollins to work as a top heel tag team and Reigns will be pushed as a top baby-face throughout the year.
Look for the turn to possibly take place at Wrestlemania.