The Vedic material distinguishes two roads out of this world. One is the road of the gods and one is the road of the fathers, and they do not lead to the same place. Yama, in the funeral hymns, is the first mortal who died and so the first to find the way, which is why he is king of the fathers rather than a judge of them: he is not sentencing anybody, he is the one who went first and knows the route. The dead man is told to go by the path the fathers went, past the two dogs, to a place of light and pasture where his own people are waiting.
The Upanishads take those two roads and turn them into two destinies. The road of the gods leads out and does not return. The road of the fathers leads to the moon, and from the moon back into rain, into plants, into food and into a new birth. A geography becomes a doctrine of rebirth, and the fathers, who in the older material had simply arrived somewhere good, become a stage in a circuit. What had been the desirable destination is now the one that comes back round.
That reframing did not stop the rites. It is one of the more striking continuities in Indian religion that a practice designed to settle the dead in a permanent afterlife carried on unchanged inside a system that had redefined the afterlife as temporary. The offering is still made, the fathers still receive it, and the doctrine and the ritual coexist without either being adjusted to fit the other.