Shift fear up the chain of command: why are general managers afraid to order their managers to order their batters to bunt against the shift?

Maybe former players like Oakland GM Billy Beane should not be general managers any more than field managers should not be former players.  That's the next logical conclusion from the previous post:

Billy Beane, field managers should not be former players. Wake the heck up!  Wednesday, July 9, 2014

Billy Beane October 7, 2010 by Leaders Event from London, United Kingdom via Wikimedia Commons