most corporate places have these sorts of rules. It is easy to quickly admonish them for this fact, but i would put in place the same policies if i was in their position as head of a corporation or similar situation.
When you run your own business and personally know all the employees, it's probably not as big of a deal. But when you run a business as large as Circle K, Wal-Mart, Target, 7-Eleven, etc, it's different.
There are a lot of legal, insurance and safety reasons why these strict no-gun policies are in place.
You and i, the enthusiasts, might be very safe with our firearms. But a lot of people do not take such a high interest and just pack heat 'for protection' with little interest or ability to obtain quality training or study relevant literature. When you're a massive corporation(and military guys might know what i'm talking about), you have to set everything up for the dumbest stack of bricks in your organization. otherwise it is a risk for everyone.
Realistically, your chances of an accidental discharge and potentially striking someone, yourself or damaging property are a lot higher than your chances of getting to shoot a robber. I think these risks can be lowered with training and education, but we're talking about the average permit holder.
99% of the time, the robbers just take the cash and go anyway. Bringing a gun into that situation doesn't make much sense. Give them the cash, and let insurance replace it. Have people been shot after complying? sure, but that's relatively rare.
Another thing is the liability. all those risks have to be born by the business, they're responsible for everything that goes on in there.
Dumbass cashier has an accidental discharge. the establishment is liable for that.
Cashier shoots robber who turns out to have been using a toy gun/no gun at all. Store is(stupid but true) potentially liable in some states for that. Especially in these nationwide/multi-national corporations, it's a risk they don't want to take. Cashier potentially causes deadly situation where she dies or is seriously injured. Establishment is liable. Cashier lacks common sense and does something stupid with her gun, Establishment liable.
They're not in the business of training folks and don't know what risks they're adopting by letting employees carry guns. That's a lot of risk and liability. There are usually rules in these places about how much money can be in the drawer. maybe ~50-75 bucks or something. Not much. Insurance will replace all of it if they're robbed.
a lawsuit could potentially be millions of dollars per incident. Just bad business.
The business would probably also have to license and insure employees if they were going to permit them to have firearms. I think their insurance costs would actually significantly rise. might not seem like a lot, but in a competitive business it could drive them out of the market.
if you want companies to allow concealed firearms on their premises, you'd have to pretty much drastically reform liability, insurance laws and so on in order for it to make sense from the corporate point of view.
In the end, Cost/Benefit doesn't add up. The benefit of allowing employees to defend themselves with firearms is a lot higher than banning them.