Earlier quoted context omitted.
Why do the dinosaurs always escape in Jurassic Park? Is it because the mathematics of chaos theory dictate that life always finds a way? Or is it because nobody pays to see a movie where a couple of brats go on an uneventful vacation to a dinosaur zoo? It's definitely the latter, but through the power of repetition people started to believe it was the former.
Neither. It's because it's extremely difficult to keep large animals confined indefinitely through all circumstances. Ask any farmer with livestock. The bigger they are, the more capable they are of ignoring whatever fencing/obstacles you put in the way.
That last point is another place where I expect a huge fiction-reality gap. If I pay to watch a movie about a dinosaur getting loose, I want to see it shrug off bunker-busting missiles from fighter jets, with big fireball explosions and people jumping in the air and the hero magically surviving. I don't want to see a short, sad walk down to the city park where they try and fail for an hour to coax it back and ultimately decide that they have to shoot it with a slightly larger than average rifle. That's the boring and horrible but realistic scenario.
There's nothing wrong with the movie scene not being realistic, but there is something wrong with blindly assuming that the movie scene is realistic.