This trope would be an “inclusive” one, actually making up a series of smaller tropes. Everyone knows there are certain rules to surviving a horror film or a spy film or occasionally an action film. Monster films also have their own set of rules in regards to the monsters themselves, who go against all known biological science. Most of these also apply to “creature features”, ones where an animal has been mutated or enraged or is just a normal deadly predator one would find on Earth (like tigers or bears) than a monster.
All Monsters have Diabetes – It doesn’t matter if the monster just scarfed down a big meal…it has to eat again immediately. While in the wild, a meat-eating predator would just find a quiet place to chill and sleep off the meal or would bury or stash whatever it couldn’t eat and just guard that, monsters in movies treat humans like Pringles…they can’t have just one. They immediately go to gobble up another with undiminished enthusiasm. That first human went right through them. Humans, apparently, are the “Chinese food” of the monster world.
F**k the Surface Area to Volume Ratio – According to well-established biological science, the bigger you get, the slower your metabolism due to retaining heat due to exponentially bigger volume to surface area. Therefore, something tiny like a mouse eats far less of its body weight than an elephant would. Giant versions of the creatures apparently never got the message. Assuming the giant creature doesn’t crush itself under the weight of its own skeleton (which it would in real life), it has to eat just as much of its body weight if not more (see previous condition) to stay alive.
Humans are the Rarest of All Delicacies – Even if a monster has plenty of other food sources to go around, perhaps even ones more abundant and nutritionally valuable than humans, it will still always preferentially go after humans. For some reason, monsters are ideally suited to metabolize humans better than anything else…which usually makes no sense because the monster almost always developed in an environment void of humans (see further below). Not only that, but regardless of the amount of effort and energy it needs to expend to get through a vehicle or past a barricade or whatever other defense the humans erected, or regardless of if past encounters with humans led to pain or injury, the monster will continue to try to go after the human as long as it takes and as hard as it takes as opposed to looking for a different, easier meal or even a different human in some cases.
Darwinian Errors – Monsters/giant creatures that are native to Earth (aliens don’t count) always develop in a state of geographic isolation and apart from human civilization. Why? Because it’s obvious we’d be f**ked if they didn’t. Monsters/giant creatures always seem to be ideally suited to kill humans and prey on them. They even seem to be able to anticipate human thoughts and behavior to make them even easier to eat. Clearly, they would be the dominant life form on Earth if some act of chance hadn’t happened. (Nowhere is this more clear than in the Jurassic Park franchise, in which after three movies the score is Dinos: 50, Humans: 0, since many humans have become dino food while the humans have yet to even stomp a Compsagnathus to death.)
Water-Bear-Like Dormancy – This is the natural consequence of all of the above. If the monsters haven’t had contact with humans since the day human tribesman wandered wherever yet exclusively prey on humans, the only natural conclusion to a native Earth monster is that they can go dormant for hundreds, even thousands, of years at a time.
Evolve in Seconds! – This rarely occurs, but when it does it makes every biologist roll their eyes. Natural selection takes an exceedingly long time. If it didn’t, we’d never have to worry about environmental concerns because every plant and animal would adapt in a couple years or decades to whatever humans screwed up. Yet Hollywood seems to think evolution takes somewhere on the order of a couple years at most to a couple minutes at least in something that would make Lamarck raise his eyebrow. Somehow predators are able to evolve to kill humans over an extremely short period of time. The two best examples ironically involve normally benign things…plants. In “The Happening”, somehow all of Earth’s trees were able to evolve virtually overnight to secrete a scent that drives humans to suicide…which is completely, utterly, and totally impossible and ridiculous, especially since even the most neurotoxic plants in the world can’t make their predators do intentionally suicidal behavior through pollen. Then there’s “The Ruins”, in which somehow a predatory vine can mimic a cell phone signal. …I’m not even going to bother explaining how that makes as much sense as me turning into a 100 foot tall mountain of spaghetti and meatballs and devouring Hoboken, New Jersey in one bite. If you can’t see it already, then I’m surprised you don’t think “The Cat in the Hat” was based on a true story.