Because Dan Snyder's the owner and can't fire himself. He's been through 6 head coaches and god knows how many quarterbacks since buying the 'Skins, many of whom had either stellar track records coming in or went on to great things post-Redskins.

He's the common denominator but can't manage to extricate himself.

Even though it was obvious that Shanahan wanted out, the players were crap and Snyder should be shipped off to another galaxy.