Why do security policies and procedures differ from airport to airport?

Why do security policies and procedures differ from airport to airport?

We really try to keep security policies and procedures consistent from airport to airport. I will tell you that as of August 10th, all shoes come off in every airport. No matter what kind of shoe you're wearing, the shoes will come off. There was some inconsistency from airport to airport, really depending on which day you flew. We try to inject some unpredictability into the system. We don't want the bad guys to know everything we're doing, so I think passengers would agree to be inconsistent here and there would be appropriate, because if they know everything we're doing then they can certainly find out how to get around it.