Divine Beasts are very magical beings; it's inevitable, as every single one is born from nature, and they just can't help but be magical.
Divine Beasts don't need to cultivate. As long as they grow naturally, they can ultimately reach the limit determined by their bloodline.
For instance, the Four Divine Beasts belong to the Chaos Realm, and most Divine Beasts are in the Black Cave Realm, but none are of the Comet or Milky Way level. That would be too weak and an insult to the term Divine Beasts.
Divine Beasts are powerful, but their offspring may not be.
Heaven-Earth Divine Beasts are unique, but to have offspring, they inevitably need to mix bloodlines, reducing the purity of their blood.
Like the Azure Dragon Clan, below the Old Dragon, there was only one Second Ancestor in the Chaos Realm, but compared to the Old Dragon, it falls far, far short.
