Harper does not want to be under WWE contract any more. He is not an employee, but an independent contractor as are all WWE Superstars. However, the company won’t let him go.
Instead of granting Harper’s release request, WWE is adding on six months to his contract from when he was out of action after wrist surgery. The company wasn’t using him anyway as his Bludgeon Brother partner Rowan was out with an injury so Harper elected to get the surgery.
Dave Meltzer mentioned on Wrestling Observer Radio that WWE had planned a feud between Sami Zayn and Harper. They nixed this rivalry for no apparent reason though.
It is not 100% clear if canceling his feud with Sami Zayn was the last straw for Harper, but it probably didn’t help him want to stay with WWE.