Demons and deities belonged to two different camps, and they were two completely different types of higher beings.
For a deity to gain strength, apart from having to comprehend laws of nature themselves, they also had to spread their faith. The more abundant their supply of power of faith was, the faster they would gain strength.
Therefore, the number of power of faith domains one had was an important indicator of a deity's strength and status.
It was a different case for demons in comparison.
Firstly, demons didn't need power of faith. They needed only to cannibalize one another or devour demons or deities of a higher level than them, and they would be able to strengthen themselves.
This was the simplest and most straightforward way—as well as what most demons did—for a demon to strengthen itself.
Apart from that, demons also had another way to strengthen themselves, and that was—to occupy existential planes.
