Isonomia would also explain why there can't be just one god.
Probably also the rule that "nature never creates only one thing of a kind," which is probably related but probably separate.
On the Nature of the Gods:
“Moreover there is the supremely potent principle of infinity, which claims the closest and most careful study; we must understand that it has in the sum of things everything has its exact match and counterpart. This property is termed by Epicurus isonomia, or the principle of uniform distribution. From this principle it follows that if the whole number of mortals be so many, there must exist no less a number of immortals, and if the causes of destruction are beyond count, the causes of conservation also are bound to be infinite."