Monsters are creatures infused with (and mutated by) Chaos Energy, which both grants them "magic" and a sixth sense called, appropriately enough, Chaos Sense.
However, magic in my world functions on two principles: balance and flow. Balance causes magic to diffuse from areas of high to low concentration, thereby spreading the influence of Elemental energy out instead of concentrating it in one place. The Principle of Flow, however, limits spreading, as magic is attracted to magic of the same type as itself. In other words, Fire Magic is drawn to Fire Magic.
The end result is something like spilling water on a table; give it time, and the water will stop spreading, forming one aqueous blob on your tabletop. Magic spreads to fill the space around it, but it doesn't move too far from its source. Makes sense, right?
However, this also has some pretty big ramifications for monsters:
1. Flow: Thanks to the Principle of Flow, monsters are attracted to monsters of the same Element as they are (firesnakes are drawn to fire dragons, for example), but more especially to their own kind. This may not seem a big deal, but here's the thing: since magic attracts magic, monsters have an overwhelming preference for preying on other monsters.
2. Balance: Just as hot objects radiate heat, magical creatures radiate magic, causing a more or less uniform spread of magic in an area.
3. Synergy: This is yet another Principle of Magic, and how it works is simple: magic bolsters and enhances magic of its own kind.
If this doesn't make sense, here's an example, a metaphor: We have a Pyromancer, Alice. In the AU, she's a bowl of chocolate ice cream. Alice=Fire Mage=Chocolate Ice Cream. Alice meets a Giant Firesnake and, being a snake fan, she lets it coil around her. It's magic synergizes with her own, increasing both their power. Firesnake=Chocolate Syrup. Chocolate Syrup+Chocolate Ice Cream=2x the chocolatey goodness. Just like chocolate syrup makes chocolate ice cream better than it could be alone (and vice versa), the firesnake's fiery aura makes Alice the Pyromancer stronger than she'd be on her own.
Because of this, monsters find they get a boost (not just an energy boost, their speed, power, and durability are increased as well) from hanging around monsters of the same element, which is why firesnakes hang around fire dragons. This boost is especially strong between members of the same species, which is why monsters tend to be found in groups, if not in pairs, and are generally not alone. Exceptions are boss monsters, or any large and powerful monsters, as their magical and biological needs necessitate they keep their territory all to themselves and fight off other members of their kind.
Anyway, if a monster was to kill and/or eat their own kind, or to eat their own kind's Drops, they'd gain this boost from the Remnants or lingering essence of their species, and this boost stacks. This would seem to encourage cannibalism, if not interspecies combat, so why are monsters not known for either?