Because in 1989 or 1990 a former PSA ramp rat lost his job, the next day he proceeded to bring a handgun to the office. Didn't kill anyone there he boarded the flight killed the crew. causing a crash. Yes the crew going through security would have stopped it. Since the guy that actually did it went through the ramp agent door. So it makes no sense to me, there are still places where we dont go through security but it gets smaller every year.