It is an open 'secret' that most national chain stores (including 7-11) have a 'no resistance' policy toward armed robbery. It is in the employee policy manuals. Employees are instructed to offer no resistance of any kind and to cooperate completely with any individual who robs the store with any kind of weapon. This includes forbidding employees to follow the thief out the door after the robbery to try to get a look at the license plate number or even a description of the getaway car.
These policies are in place for employee safety, insurance, and liability reasons.
If McClean had fired his weapon and killed or wounded the thief there would be the potential for a huge lawsuit.