Compared to the indigestible souls of their own kind, the souls of creatures from the Material Plane are delicious and easy to digest, favored by almost all demons.
It can be understood this way: demons devouring other demons' souls can also enhance their own strength, but it's like eating a breadstick as hard as a stone; it can be eaten, but it's unpleasant and hard to digest.
However, consuming souls of humans or dwarves is like eating vegetarian dishes with added meat; relatively tasty and nutritious.
Eating the souls of elves, fairies, or giant dragons is even more incredible, akin to eating premium meat dishes, with the stronger the soul, the more nutritious it is.
Goblins, giant demons, and jackal wolfmen's souls, relatively speaking, are somewhat inferior, but are generally tastier than demon souls, at least soft-bread level.
