There's never been a bomb in the maze/lines before security. Why not?

A small comment that will probably go mostly unnoticed, but this question has always bothered me too and it's a second opportunity inside of an hour to talk about working at Disneyland post 9/11. We instituted bag checks at the intake turnstiles for the first time after that, and the result was enormous lines that backed up all the way to the streets. It left me wondering why nobody just detonated a bomb or fired the entire magazine of an Uzi into the crowd waiting to get into the park. You could still kill anywhere from hundreds to thousands of people, it's still at Disneyland. What were we really accomplishing by making it less likely to happen in the park, but possibly making it even easier to happen right outside, given the gridlock, how tightly everyone was packed, and the impossibility of hiding anywhere or running away?