I like to think of Behemoths like dragons in typical fantasy tropes. They're so massive that they live life on a different scale. Some might work with Beasts, but most don't consider them worth thinking about. What's a eating a few squirrels to a wolf? 

For an example of a Behemoth working in tandem with Beasts, there are a couple in Apawthecaria, a sister game to Scurry. Boldheart the Sea Eagle helps taxi smaller Beasts to-and-fro from Summit, though for a fairly hefty price in food.