Sanchez has talents as well as faults. As with all players, it is in the best interest of everyone involved that you play to the former and do your best to eliminate or hide the latter. For whatever reason, Rex and the coaching staff do not do this with Sanchez. Why is anybody's guess.
Maybe we'll find out when Rex and Sanchez are both gone. Make no mistake, Rex will not be successful with this approach, nor will Sanchez. And I say that as someone who was a HUGE Rex supporter.