Each of the gods are not only gods, but also parts of the world.
Well, clearly this is a silly statement, as even Varro understands. "And the same is true with respect to all the rest, as is true with respect to those things which I have mentioned for the sake of example. They do not explain them, but rather involve them. They rush hither and thither, to this side or to that, according as they are driven by the impulse of erratic opinion; so that even Varro himself has chosen rather to doubt concerning all things, than to affirm anything."
That is, the pagans do not actually articulate a clear theological defense of the gods, they simply keep them in perpetual motion so that one can never pin them down long enough to discuss their truth or falsehood. As a result the more thoughtful philosophers such as Varro have retreated into an intellectual skepticism while maintaining the facade of piety.
It is much more likely that the origin of these gods was in stories of human kings which grew with the telling over the centuries.