All it takes is hitting a webpage to break into this Arizona airport. They even give you directions on how to break into the gate into prohibited areas. This image comes right from that site:
In summary: To open the gate, use the lock box combo '215' to get the magstripe card, and then use the card in the reader.
Even before 9/11/01, US Airports were legislated to improve airport security requirements drastically. This did not just apply to big airports, either. Tiny, rural municipal airports were subject to the same stringent (federal) access control requirements.
Areas like the tarmac and runways not only had to be fenced, but access control systems are required to keep unauthorized people out. The problem is keeping up with every potential user and issuing credentials. Airports spent money to upgrade systems, but lack or are unwilling to spend money to administrate them properly.
As a result, mandatory security measures are seen as an inconvenience, not a benefit. You end up with access systems that really serve no purpose.