With Divine Power, comes Divine Domains. The general rule is that the greater the power, the more domains.
Divine Domain is the primary area of influence for a Higher Power. It corresponds to the domains that priests can acquire if they worship a particular god. It is also an aspect of areas, worlds, and systems. It gives a boon for those in these areas, like a tendency for tyrannical rule on Avalas and order on Mechanus.
Higher Powers acquire more domains as they ascend the Matrix of Divine Power. The number they get is a starting number, because gods, fiends and anything considered a Higher Power can acquire domains by utterly defeating another higher power or primordial lord and taking one of their domains or in the case of primordial lords, their energy and convert it into a domain. This tactic of taking a domain by killing another is more commonly done by evil and neutral beings. A goodly higher power would not imitate a conflict on the pretext of acquiring a domain by totaling eliminating another. Ares was the first god to crush another upstart deity and take one of his domains, along with the other god's entire worshipper base.