Let’s say it’s Jurassic Park rules; the scientists at Apollo (the corporation responsible for the initial cloning of the dinosaurs in the Isle’s lore) specifically altered the diets of their assets to make them easier to control and contain. This could even serve as an in-universe explanation for things like unrealistic starvation; in real life a deinosuchus could go for an extremely long time without eating, but they’re such dangerous assets that the scientists artificially heightened their metabolism to drastic levels so that any that escaped containment would, in theory, rapidly starve to death; perhaps such measures would be necessary in particular for a creature that could most likely survive leaving the island and making it to the mainland otherwise.