I imagine the lack of Lingua Franca is due to the vast differences in sensory abilities. Without something that can effectively be shared, it doesn’t work well. In the end, you result to creating a mishmash of languages you do know to try and get your thoughts across. It also looks like the continent the monsters live on is pretty scarce on resources. That probably forces the monsters to prioritize in communication to trade for what they need in order to survive. Any kind of hostility could cause you to lose out on a trade, and therefore not survive.
Humans have a huge variety of sounds that we can make with our throat, cheeks, tongue, teeth, and lips, but our range for hearing is pretty small. We also have a pretty limited range for what we see, and an even smaller range for smelling.
Werewolves communicate mostly through smelling/tasting, but also verbal and visual. They are limited by their vocals, though.
Lizard people don’t have much of an ability to smell and are also limited vocally (not as much as the werewolves, but not as flexible as humans). They also have zero sense of taste. But they DO have a better ability to see colors.
Kraken can’t communicate vocally at all, relying on changing colors.
Harpy can communicate vocally, but the pitch at which they speak is so high most other species can’t hear them. And they move too quickly for other species to efficiently communicate using that body language. Harpies likely don’t have much of a sense of smell, either.