Maybe criminals and banks do not mix very well. Citizens with concealed carry permits commit less gun crimes than does law enforcement.
Sorry, I used to be on a first-name basis with some bank security guards. That is the only perspective I intended to bring . . . if one of them saw a gun peeking out of my waistband (and I was a stranger), then the outcome would not be as pretty as people would like to believe when discussing blackboard-theory.