Source: PWInsider Elite
As noted, Justin Gabriel quit WWE this past weekend, after signing with WWE in 2008.
Gabriel requested his release from WWE officials because he realized he was in a position where the company was not going to do anything else with him beyond Superstars, Main Event and NXT. Gabriel being pulled from the Royal Rumble main event may have been the last straw.
Gabriel wanted more than what WWE was giving him for his pro wrestling career and is looking forward to working the indies. Gabriel will be working as PJ Black from here on out.