The movie Jurassic Park was a success because the actual Jurassic Park was such a disaster. Without the weak infrastructure and slapdash safety measures implemented by Hammond and Co., the film would have been a pleasant but ultimately boring infomercial peppered with Jeff Goldblum's awkward laughter. We want things to go wrong in a Jurassic movie, for humanity to learn a lesson about the consequences of playing God, etc -- but that hubris and stupidity leading up to dinosaurs eating people on the shitter has to be somewhat believable.
Case in point: In the first movie, we see that the park is equipped with gargantuan electrified fences. It seems believable that this kind of heavy equipment could keep prehistoric carnivores in check.
Of course, the whole plan falls apart when humanity a) underestimates the ingenuity and determination of nature's creatures and b) underestimates Dennis Nedry's capacity to be an asshole. A perfect storm of unruly animals, trecherous employees and uh, a perfect storm proves undoes every one of Jurassic Park's security countermeasures.
You'd think that when it came to Jurassic World, humanity would take a few cues from that time 20 years ago when everything went horribly, murderously wrong, but it seems like they actually have dialed down safety measures compared to the old park. The most glaring flaw: From what we see in the movie, Jurassic World has barely any fences or walls. Sure, the raptors and the Indominus Rex have their own fortified enclosures, but outside of those there isn't much preventing the dinosaurs from rampaging through the restricted area down into the theme park.
The biggest barrier we see is the gate for the gyrosphere area, which pales in comparison to those huge electrified fences in Jurassic Park.
The GPS implants imply some kind of invisible fence technology at work, but the folks at Jurassic World had to have known that wouldn't be enough. If just one tracker went on the fritz, there'd be nothing stopping a triceratops from goring up to three park guests simultaneously. Even though this is a world where people are stupid enough to build another Jurassic Park to begin with, there's no excuse for not building multiple failsafes into their security protocols.
Judging by the map of the island, you'd think that at some point we'd have seen a giant Attack On Titan-sized wall surrounding the Restricted Area, but nothing like that appears in the movie -- probably because it would have put a damper on the I-Rex's rampage
Then again, Jurassic World would have never had this problem in the first place if it weren't for a handful of idiots.
Though the central calamity of Jurassic Park was brought on by a multitude of factors, the entire crisis of Jurassic World can be blamed on one pivotal moment. Yes, the cunning Indominus Rex hatches a surprisingly complex plan of escape, but it wouldn't have worked if not for the fact that every human in the area was popping Stupid Pills. Remember, the I-Rex fools everyone into thinking it's not in its enclosure by thermal camoflauge and its own personal Klingon cloaking device, while purposefully scratching up the cement wall to give the impression that it had already escaped. Baffled, the park's staff of yahoos (which includes Chris Pratt's Owen) saunter into the supposedly empty enclosure to try to figure out what happened.
Naturally, it is soon revealed that the I-Rex was in the cage all along.
The command center comes to this conclusion by zeroing on the I-Rex's tracker, which at this point has not yet been excised from its flesh. But it's too late -- three people have already ventured into the paddock to investigate, and are stuck in the enclosure with the genetic monstrosity. For supposed dinosaur experts, this is by far the dumbest move anyone could make. The very first thing anyone would do is check the GPS coordinates of the dinosaur to see if it had truly escaped. When you think there might be a fire on the other side of a door, you check the knob for heat before opening it. But the characters in Jurassic World seem like they'd prefer walking into the open blaze just to see how flame retardant their cargo vests are.
There was nothing to be gained from going out into the paddock. The scratches they were investigating could easily be seen from the safety of the control room, at what looks like a better vantage point.
Because of this massive oversight, because Claire and Owen didn't perform the most nominal of checks before entering the most dangerous area of the park, the I-Rex was unleashed.
Then again, if the dummies at JW weren't such dumb dummies, there wouldn't be a movie. At best, we'd get a drama about two teen boys grappling with their parents' divorce while dinosaurs roam in the background. Don't get me wrong, I'd probably also watch that, but I think we can all agree that dinosaurs are at their best when they're terrorizing an island full of tourists.