This comes out of nowhere but really isn’t all that shocking:
Harper spent much of his run in WWE working in a team alongside The Wyatt Family, then, later, with Erick Rowan. Most recently, he took significant time off to heal up some injuries after Rowan was hurt and had to do the same. His return came at WrestleMania Axxess in a match that meant an awful lot to him, as he explained in a lengthy post on social media.
He appeared in the Andre the Giant Memorial Battle Royal but was hardly showcased and it seems clear WWE has no plans to give him a run at the top. At 39-years-old, there’s no real time to waste as far as accomplishing career goals, so he wasn’t left with much of an option here.